 Quartz is the most abundant mineral in the Earth's continental crust. It has a hexagonal crystal structure made of trigonal crystallized silica (silicon dioxide, SiO2), with a hardness of 7 on the Mohs scale. Density is 2.65 g/cm³. The typical shape is a six-sided prism that ends in six-sided pyramids, although these are often twinned, distorted, or so massive that only part of the shape is apparent from a mined specimen. Additionally a bed is a common form, particularly for varieties such as amethyst, where the crystals grow up from a matrix and thus only one termination pyramid is present. A quartz geode consists of a hollow rock (usually with an approximately spherical shape) with a core lined with a bed of crystals.Varieties Quartz is one of the world's most common crustal minerals and goes by a bewildering array of different names. The most important distinction between types of quartz is that of macrocrystalline (individual crystals visible to the unaided eye) and the microcrystalline or cryptocrystalline varieties (aggregates of crystals visible only under high magnification). Chalcedony is a generic term for cryptocrystalline quartz. The cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is a secondary identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. This does not always hold true. Not all varieties of quartz are naturally occurring. Prasiolite, an olive colored material, is produced by heat treatment. Although citrine occurs naturally, the majority is the result of heat-treated amethyst. Carnelian is widely heat-treated to deepen its color. Because natural quartz is so often twinned, much quartz used in industry is synthesized. Large, flawless and untwined crystals are produced in an autoclave via the hydrothermal process: emeralds are also synthesized in this fashion. Quartz occurs in hydrothermal veins and pegmatites. Well-formed crystals may reach several meters in length and weigh hundreds of kilograms. Erosion of pegmatites may reveal expansive pockets of crystals, known as "cathedrals." Quartz is a common constituent of granite, sandstone, limestone, and many other igneous, sedimentary, and metamorphic rocks. Some quartz crystal structures are piezoelectric and are used as oscillators in electronic devices such as quartz clocks and radios. Lechatelierite is an amorphous silica glass SiO2 which is formed by lightning strikes in quartz sand. History The name "quartz" comes from the German "Quarz", which is of Slavic origin. Quartz is the most common material identified as the mystical substance maban in Australian Aboriginal mythology. Roman naturalist Pliny the Elder believed quartz to be permanently frozen ice. He supported this idea by saying that quartz is found near glaciers in the Alps and that large quartz crystals were fashioned into spheres to cool the hands. He also knew of the ability of quartz to split light into a spectrum. Nicolas Steno's study of quartz paved the way for modern crystallography. He discovered that no matter how distorted a quartz crystal, the long prism faces always made a perfect 60 degree angle. Piezoelectricity Quartz is also a type of piezoelectric crystal that creates electricity through a process called piezoelectricity when mechanical stress is put upon it. One of the earliest uses for a quartz crystal was a phonograph pickup. Today, one of the most ubiquitous piezoelectric uses of quartz is as a crystal oscillator -- in fact these oscillators are often simply called "quartzes". This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Quartz. |
Wednesday, December 6, 2006
Monday, November 6, 2006
Jewelry: Ruby
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Ruby. |
Sunday, October 22, 2006
Jewelry: Filigree
fil·i·gree (fĭl'ĭ-grē')
Delicate and intricate ornamental work made from gold, silver, or other fine twisted wire.
An intricate, delicate, or fanciful ornamentation.
A design resembling such ornamentation: filigrees of frosting on a cake.
Filigree (formerly written filigrann or filigrane) is a jewel work of a delicate kind made with twisted threads usually of gold and silver.
The word, which is usually derived from the Latin filum, thread, and granum, grain, is not found in Ducange, and is indeed of modern origin. According to Prof. Skeat it is derived from the Spanish filigrana, from "filar", to spin, and grano, the grain or principal fiber of the material.
Though filigree has become a special branch of jewel work in modern times it was anciently part of the ordinary work of the jeweler. Signor A. Castellani states, in his "Memoir on the Jewelry of the Ancients" (1861), that all the jewelry of the Etruscans and Greeks (other than that intended for the grave, and therefore of an unsubstantial character) was made by soldering together and so building up the gold rather than by chiseling or engraving the material.
The art may be said to consist in curling, twisting and plaiting fine pliable threads of metal, and uniting them at their points of contact with each other, and with the ground, by means of gold or silver solder and borax, by the help of the blowpipe. Small grains or beads of the same metals are often set in the eyes of volutes, on the junctions, or at intervals at which they will set off the wire-work effectively. The more delicate work is generally protected by framework of stouter wire. Brooches, Star of David, earrings and other personal ornaments of modern filigree are generally surrounded and subdivided by bands of square or
flat metal, giving consistency to the filling up, which would not other-wise keep its proper shape. Some writers of repute have laid equal stress on the glum and the granuna, and have extended the use of the term filigree to include the granulated work of the ancients, even where the twisted wire-work is entirely wanting. Such a wide application of the term is not approved by current usage, according to which the presence of the twisted threads is the predominant fact.
The Egyptian jewelers employed wire, both to lay down on a background and to plait or otherwise arrange d jour. But, with the exception of chains, it cannot be said that filigree work was much practiced by them. Their strength lay rather in their cloisonne work and their molded ornaments. Many examples, however, remain of round plaited gold chains of fine wire, such as are still made by the filigree workers of India, and known as irichinopoly chains. From some of these are hung smaller chains of finer wire with minute fishes and other pendants fastened to them.
In ornaments derived from Phoenician sites, such as Cyprus and Sardinia, patterns of gold wire are laid down with great delicacy on a gold ground, but the art was advanced to its highest perfection in the Greek and Etruscan filigree of the 6th to the 3rd centuries BC. A number of earrings and other personal ornaments found in central Italy are pre-served in the Louvre and in the British Museum. Almost all of them are made of filigree work. Some earrings are in the form of flowers of geometric design, bordered by one or more rims each made up of minute volutes of gold wire, and this kind of ornament is varied by slight differences in the way of disposing the number or arrangement of the volutes. But the feathers and petals of modern Italian filigree are not seen in these ancient designs. Instances occur, but only rarely, in which filigree devices in wire are self-supporting and not applied to metal plates.
The museum of the Hermitage at Saint Petersburg contains an amazingly rich collection of jewelry from the tombs of the Crimea. Many bracelets and necklaces in that collection are made of twisted wire, some in as many as seven rows of plaiting, with clasps in the shape of heads of animals of beaten work. Others are strings of large beads of gold, decorated with volutes, knots and other patterns of wire soldered over the surfaces. (See the "Antiquites du Bosphore Cimmerien", by Gille, 1854; reissued by S. Reinach, 1892, in which will be found careful engravings of these objects.) In the British Museum a sceptre, probably that of a Greek priestess, is covered with plaited and netted gold wipe, finished with a sort of Corinthian capital and a boss of green glass.
It is probable that in India and various parts of central Asia filigree has been worked from the most remote period without any change in the designs. Whether the Asiatic jewelers were influenced by the Greeks settled on that continent, or merely trained under traditions held in common with them, it is certain that the Indian filigree workers retain the same patterns as those of the ancient Greeks, and work them in the same way, down to the present day. Wandering workmen are given so much gold, coined or rough, which is weighed, heated in a pan of charcoal, beaten into wire, and then worked in the courtyard or verandah of the employer's house according to the designs of the artist, who weighs the complete work on restoring it and is paid at a specified rate for his labor. Very fine grains or beads and spines of gold, scarcely thicker than coarse hair, projecting from plates of gold are methods of ornamentation still used.
Passing to later times we may notice in many collections of medieval jewel work (such as that in the South Kensington Museum) reliquaries, covers for the gospels, etc., made either in Constantinople from the 6th to the 12th centuries, or in monasteries in Europe, in which Byzantine goldsmiths' work was studied and imitated. These objects, besides being enriched with precious stones, polished, but not cut into facets, and with enamel, are often decorated with filigree. Large surfaces of gold are sometimes covered with scrolls of filigree soldered on; and corner pieces of the borders of book covers, or the panels of reliquaries, are not infrequently made up of complicated pieces of plaited work alternating with spaces encrusted with enamel. Byzantine filigree work occasionally has small stones set amongst the curves or knots. Examples of such decoration can be seen in the South Kensington and British Museums.
In the north of Europe the Saxons, Britons and Celts were from an early period skilful in several kinds of goldsmiths' work. Admirable examples of filigree patterns laid down in wire on gold, from Anglo-Saxon tombs, may be seen in the British Museum notably a brooch from Dover, and a sword-hilt from Cumberland.
The Irish filigree work is more thoughtful in design and more varied in pattern than that of any period or country that could be named. Its highest perfection must be placed in the loth and lath centuries. The Royal Irish Academy in Dublin contains a number of reliquaries and personal jewels, of which filigree is the general and most remarkable ornament. The "Tara" brooch has been copied and imitated, and the shape and decoration of it are well known. Instead of fine curls or volutes of gold thread, the Irish filigree is varied by numerous designs bi which one thread 'can be traced through curious knots and complications, which, disposed over large surfaces, balance one another, but always with special varieties and arrangements difficult to trace with the eye. The long thread appears and disappears without breach of continuity, the two ends generally worked into the head and the tail of a serpent or a monster. The reliquary containing the "Bell of Saint Patrick" is covered with knotted work in many varieties. A two-handled chalice, called the "Ardagh cup" found near Limerick in 1868, is ornamented with work of this kind of extraordinary fineness. Twelve plaques on a band round the body of the vase, plaques on each handle and round the foot of the vase have a series of different designs of characteristic patterns, in fine filigree wire work wrought on the front of the repousse ground. (See a paper by the 3rd Earl of Dunraven in Transactions of Royal Irish Academy, xxiv. pt. iii. 1873.)
Much of the medieval jewel work all over Europe down to the 15th century, on reliquaries, crosses, croziers and other ecclesiastical goldsmiths' work, is set off with bosses and borders of filigree. Filigree work in silver was practiced by the Moors of Spain during the middle ages with great skill, and was introduced by them and established all over the Peninsula, whence it was carried to the Spanish colonies in America. The Spanish filigree work of the 17th and 18th centuries is of extraordinary complexity (examples in the Victoria and Albert Museum), and silver filigree jewelry of delicate and artistic design is still made in considerable quantities throughout the country.
The manufacture spread over the Balearic Islands, and among the populations that border the Mediterranean. It is still made all over Italy, and in Malta, Albania, the Ionian Islands and many other parts of Greece. That of the Greeks is sometimes on a large scale, with several thicknesses of wires alternating with larger and smaller bosses and beads, sometimes set with turquoises, etc, and mounted on convex plates, making rich ornamental headpieces, belts and breast ornaments. Filigree silver buttons of wire-work and small bosses are worn by the peasants in most of the countries that produce this kind of jewelry.
Silver filigree brooches and buttons are also made in Denmark, Norway and Sweden. Little chains and pendants are added to much of this northern work.
Some very curious filigree work was brought from Abyssinia after the capture of Magdalaarm-guards, slippers, cups, etc, some of which are now in the South Kensington Museum. They are made of thin plates of silver, over which the wire-work is soldered. The filigree is subdivided by narrow borders of simple pattern, and the intervening spaces are made up of many patterns, some with grains set at intervals.
A few words must be added as to the granulated work which, as stated above, some writers have classed under the term of filigree, although the twisted wires may be altogether wanting. Such decoration consists of minute globules of gold, soldered to form patterns on a metal surface. Its use is rare in Egypt. (See J. de Morgan, Fouilles a Dahchour, 1894-1895, pl. xii.) It occurs in Cyprus at an early period, as for instance on a gold pendant in the British Museum from Enkomi in Cyprus (10th century BC). The pendant is in the form of a pomegranate, and has upon it a pattern of triangles, formed by more than 3000 minute globules separately soldered on. It also occurs on ornaments of the 7th century BC from Camirus in Rhodes. But these globules are large, compared with those which are found on Etruscan jewelry. Signor Castellani, who had made the antique jewelry of the Etruscans and Greeks his special study, with the intention of reproducing the ancient models, found it for a long time impossible to revive this particular process of delicate soldering. He overcame the difficulty at last, by the discovery of a traditional school of craftsmen at St Angelo in Vado, by whose help his well-known reproductions were executed.
For examples of antique' work the student should examine the gold ornament rooms of the British Museum, the Louvre and the collection in the Victoria and Albert Museum. The last contains a large and very varied assortment of modern Italian, Spanish, Greek and other jewelry made for the peasants of various countries. It also possesses interesting examples of the modern work in granulated gold by Castellani and Giuliano. The Celtic work is well represented in the Royal Irish Academy in Dublin.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Filigree.
History of Jewelry: Filigree
Tuesday, September 5, 2006
Jewelry: Sapphire
Sapphire
Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. It can be found naturally as gemstones or manufactured in large crystal boules for varied applications, including infrared optical components, watch faces, high-durability windows, and wafers for the deposition of semiconductors such as GaN nanorods.
The corundum group consists of pure aluminium oxide. Trace amounts of other elements such as iron, titanium and chromium give sapphires their blue, yellow, pink, purple, orange or greenish color. Sapphire includes any gemstone quality varieties of the mineral corundum except the fully saturated red variety, which is instead known as ruby.
Natural sapphire
Although blue is considered the normal color for sapphire, it is found in the full range of spectral colors as well as brown, colorless, grey and black. Any sapphire other than blue or fully saturated red (ruby) is considered a fancy color sapphire.
Blue sapphire
Various shades of blue result from titanium and iron inclusions within the aluminium oxide crystal lattice. Some stones are not well saturated and show tones of gray. It is common to bake natural sapphires to improve color. This is usually done by heating the sapphires to temperatures of up to 1800°C for several hours, or by heating in a nitrogen deficient atmosphere oven for 7 days or more. On magnification the silk due to included rutile needles are visible. If the needles are unbroken, then the stone was not heated. If the silk is not visible then the stone was heated adequately. If the silk is partially broken then a process known as low tube heat was used. Low tube heat is the process where the rough stone is heated to 1300 °C for 20 to 30 minutes over charcoal. This takes out any gray or brown in the stone and improves color saturation.
Fancy color sapphire
Purple sapphires are lower in price than blue ones. These stones contain the trace element vanadium and come in a wide variety of shades. Yellow and green sapphires have traces of iron which gives them their color. Pink sapphires have a trace element of chromium and the deeper the color pink the higher the value as long as the color is going toward red of rubies.
Color change sapphire
Color shift sapphires are blue in outdoor light and purple in indoor light. Color changes may also be pink in daylight to greenish in fluorescent light. Some stones shift color well and others only partially, in that some stones go from blue to blue purple. White sapphires usually come out of the ground as light gray or brown and are then heated to make them clear. However in very rare circumstances they will be
Star sapphire
A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism. Star sapphires contain intersecting needle-like inclusions (often the mineral rutile) that cause the appearance of a six-rayed 'star'-shaped pattern when viewed with a single overhead light source. Twelve-ray stars are also found, but are less common.
A "star sapphire" ring with two diamonds on a silver band. The value of a star sapphire depends not only on the carat weight of the stone but also the body color, visibility, and intensity of the star.
Treatments
Some sapphires are heat-treated or otherwise enhanced to improve their appearance and color, though some people object to such practices and prefer natural untreated stones. Treated stones tend to be darker than untreated stones and the treatment process causes changes to the internal structure that are generally easily detected.
Mining
Sapphires are mined from alluvial deposits or from primary underground workings. Historically, most sapphires have been mined in Sri Lanka, Madagascar and Myanmar. Australia leads the world in sapphire production (as of 1987) specifically from basalt derived placer deposits in Queensland and New South Wales. Pakistan, Afghanistan, India, Tanzania and Kenya also produce sapphires. The US state of Montana has produced sapphires from the Yogo Gulch deposit near Helena. Gem grade sapphires and rubies are also found in and around Franklin, North Carolina, USA. Several mines are open to the public.
Synthetic sapphire
Synthetic sapphire crystals can be grown in cylindrical crystal ingots of large size, up to many inches in diameter. As well as gemstone applications there are many other uses:
The first ever laser produced was based on the ruby chromium impurity in sapphire. While this laser has few applications, the Ti-sapphire laser is popular due to the relatively rare ability to tune the laser wavelength in the red-to-near infrared region of the electromagnetic spectrum. It can also be easily mode locked. In these lasers, a synthetically produced sapphire crystal with chromium or titanium impurities is irradiated with intense light from a special lamp, or another laser, to create stimulated emission.
Pure sapphire ingots can be sliced into wafers and polished to form transparent crystal slices. Such slices are used as watch faces in high quality watches, as the material's exceptional hardness makes the face almost impossible to scratch. Since sapphire ranks a 9 on the Mohs Scale, owners of such watches should still be careful to avoid exposure to diamond jewelry, and should avoid striking their watches against artificial stone and simulated stone surfaces. Such surfaces often contain materials including silicon carbide, which, like diamond, are harder than sapphire and thus capable of causing scratches (Scheel 2003).
Historical and cultural references
According to Rebbenu Bachya, the word "Sapir" in the verse Exodus 28:20 means "Sapphire" and was the stone on the Ephod representing the tribe of Issachar. However, this is disputed as the sapphire of the Bible was likely lapis lazuli (Texas Natural Science Center, 2006).
Supernatural powers were attributed to gems in India. One way this was manifested was the interdependence between gems and planets. Ruby, associated with the Sun, was the Lord of Gems, for the Sun lorded over all the planets. Blue sapphire is associated with Saturn (Wojtilla, 1973), yellow sapphire with Jupiter.
- Sapphire is the birthstone associated with September.
- The 45th wedding anniversary is known as the sapphire anniversary.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Sapphire.
The History of Jewelry: Sapphires
Friday, July 7, 2006
Jewelry: Emerald
emerald, the green variety of beryl, of which aquamarine is the blue variety. Chemically, it is a beryllium-aluminum silicate whose color is due to small quantities of chromium compounds. The emerald was highly esteemed in antiquity; the stones were used for ornaments in early Egypt where some of the first emeralds were mined. The finest emeralds are found in South America in Colombia, where they have been mined for over 400 years. The gem was a favorite in pre-Columbian Mexico and Peru, where it was cut in intricate designs. The treasure taken back to Spain by early explorers included emeralds. Good emeralds are the most highly valued of gem stones. India, Zimbabwe, and Australia are minor sources of the natural stones. Synthetic emeralds are also manufactured in Germany, France, and the United States. The Oriental emerald, a different gem, is the transparent green variety of corundum.
Emerald is regarded as the traditional birthstone for May , as well as the traditional gemstone for the astrological signs of Taurus and Cancer.
According to Rebbenu Bachya, the Hebrew word "Nofech" in Exodus 28:18 means "Emerald", and was the stone on the Ephod representing the tribe of Judah. According to other commentaries, "Nofech" means "garnet", and another stone, the "Bareqet", representing the tribe of Levi, is thought to be emerald.
In some cultures, the emerald is the traditional gift for the 55th wedding anniversary. It is also used as a 20th and 35th wedding anniversary stone.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Emerald.
History of Jewelry: Emerald
Jewelry: Turquoise
Turquoise is an opaque, blue-to-green mineral that is a hydrous phosphate of copper and aluminum, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is rare and valuable in finer grades and has been prized as a gem and ornamental stone for thousands of years owing to its unique hue. In recent times turquoise, like most other opaque gems, has been devalued by the introduction of treatments, imitations, and synthetics onto the market, some difficult to detect even by experts.
The substance has been known by many names, but the word turquoise was derived around 16th century from the French language either from the word for Turkish (Turquois) or dark-blue stone (pierre turquin).[1] This may have arisen from a misconception: turquoise does not occur in Turkey but was traded at Turkish bazaars to Venetian merchants who brought it to Europe.[1] The color, however, has been employed extensively in the decorative tiles adorning Turkish places of worship and homes for hundreds of years, beginning with the Seljuks, and the association quite possibly has caused the name to take root.
Properties of turquoise
Even the finest of turquoise is fractural, reaching a maximum hardness of just under 6, or slightly more than window glass.[2] Characteristically a cryptocrystalline mineral, turquoise almost never forms single crystals and all of its properties are highly variable. Its crystal system is proven to be triclinic via X-ray diffraction testing. With lower hardness comes lower specific gravity (high 2.90, low 2.60) and greater porosity: These properties are dependent on grain size. The luster of turquoise is typically waxy to subvitreous, and transparency is usually opaque, but may be semi translucent in thin sections. Color is as variable as the mineral's other properties, ranging from white to a powder blue to a sky blue, and from a blue-green to a yellowish green. The blue is attributed to dichromatic copper while the green may be the result of either iron impurities (replacing aluminum) or dehydration.
The refractive index (as measured by sodium light, 589.3 nm) of turquoise is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a gemological refract meter, owing to the almost invariably polycrystalline nature of turquoise. A reading of 1.61–1.65 (birefringence 0.040, biaxial positive) has been taken from rare single crystals. An absorption spectrum may also be obtained with a hand-held spectroscope, revealing a line at 432 nanometers and a weak band at 460 nanometers (this is best seen with strong reflected light). Under long wave ultraviolet light, turquoise may occasionally fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and X-rays.
Turquoise is infusible in all but heated hydrochloric acid. Its streak is a pale bluish white and its fracture is conchoidal, leaving a waxy luster. Despite its low hardness relative to other gems, turquoise takes a good polish. Turquoise may also be peppered with flecks of pyrite or interspersed with dark, spidery limonite veining.
Formation
As a secondary mineral, turquoise apparently forms by the action of percolating acidic aqueous solutions during the weathering and oxidation of pre-existing minerals. For example, the copper may come from primary copper sulfides such as chalcopyrite or from the secondary carbonates malachite or azurite; the aluminum may derive from feldspar; and the phosphorus from apatite. Climate factors appear to play an important role as turquoise is typically found in arid regions, filling or encrusting cavities and fractures in typically highly altered volcanic rocks, often with associated limonite and other iron oxides. In the American southwest turquoise is almost invariably associated with the weathering products of copper sulfide deposits in or around potassium feldspar bearing porphyritic intrusives. In some occurrences alunite, potassium aluminum sulfate, is a prominent secondary mineral. Typically turquoise mineralization is restricted to a relatively shallow depth of less than 20 m, although it does occur along deeper fracture zones where secondary solutions have greater penetration or the depth to the water table is greater.
Although the features of turquoise occurrences are consistent with a secondary or supergene origin, some sources refer to a hypogene origin. The hypogene hypothesis, which holds that the aqueous solutions originate at significant depth, from hydrothermal processes. Initially at high temperature, these solutions rise upward to surface layers, interacting with and leaching essential elements from pre-existing minerals in the process. As the solutions cool, turquoise precipitates, lining cavities and fractures within the surrounding rock. This hypogene process is applicable to the original copper sulfide deposition; however, it is difficult to account for the many features of turquoise occurrences by a hypogene process. That said, there are reports of two phase fluid inclusions within turquoise grains that give elevated homogenization temperatures of 90 to 190 oC that require explanation.
Turquoise is nearly always cryptocrystalline and massive and assumes no definite external shape. Crystals, even at the microscopic scale, are exceedingly rare. Typically the form is vein or fracture filling, nodular, or botryoidal in habit. Stalactite forms have been reported. Turquoise may also pseudomorphously replace feldspar, apatite, other minerals, or even fossils. Odontolite is fossil bone or ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate vivianite. Intergrowth with other secondary copper minerals such as chrysocolla is also common.
Occurrence
Massive turquoise in matrix with quartz from Mineral Park, Arizona.Turquoise was among the first gems to be mined, and while many historic sites have been depleted, some are still worked to this day. These are all small-scale, often seasonal operations, owing to the limited scope and remoteness of the deposits. Most are worked by hand with little or no mechanization. However, turquoise is often recovered as a byproduct of large-scale copper mining operations, especially in the United States.
Iran
For at least 2,000 years, the region once known as Persia, has remained the most important source of turquoise, for it is here that fine material is most consistently recovered. This "perfect color" deposit that is blue naturally and turns green when heated because getting dehyrated is restricted to a mine-riddled in Neyshabur,[3][4][5] 2,012-metre mountain peak of Ali-mersai, tens of kilometers far from Mashhad, the capital of Khorasan province, Iran. A weathered and broken trachyte is host to the turquoise, which is found both in situ between layers of limonite and sandstone, and amongst the scree at the mountain's base. These workings, together with those of the Sinai Peninsula, are the oldest known.
Iranian turquoise is often found replacing feldspar. Although it is commonly marred by whitish patches, its color and hardness are considered superior to the production of other localities. Iranian turquoise has been mined and traded abroad for centuries, and was probably the source of the first material to reach Europe.
Sinai
Since at least the First Dynasty (3,000 BCE), and possibly before then, turquoise was used by the Egyptians and was mined by them in the Sinai Peninsula, called "Country of Turquoise" by the native Monitu. There are six mines in the region, all on the southwest coast of the peninsula, covering an area of some 650 km². The two most important of these mines, from a historic perspective, are Serabit el-Khadim and Wadi Maghareh, believed to be among the oldest of known mines. The former mine is situated about 4 kilometres from an ancient temple dedicated to Hathor.
The turquoise is found in sandstone that is, or was originally, overlain by basalt. Copper and iron workings are present in the area. Large-scale turquoise mining is not profitable today, but the deposits are sporadically quarried by Bedouin peoples using homemade gunpowder. In the rainy winter months, miners face a risk from flash flooding; even in the dry season, death from the collapse of the haphazardly exploited sandstone mine walls is not unheard of. The color of Sinai material is typically greener than Iranian material, but is thought to be stable and fairly durable. Often referred to as Egyptian turquoise, Sinai material is typically the most translucent, and under magnification its surface structure is revealed to be peppered with dark blue discs not seen in material from other localities.
In proximity to nearby Eilat, Israel, an attractive intergrowth of turquoise, malachite, and chrysocolla is found. This rock is called Eilat stone and is often referred to as Israel's national stone: it is worked by local artisans for sale to tourists.
United States
A selection of Ancestral Puebloan (Anasazi) turquoise and orange argillite inlay pieces from Chaco Canyon (dated ca. 1020–1140 CE) show the typical color range and mottling of American turquoise.
Bisbee turquoise commonly has a hard chocolate brown colored matrix, and is considered some of the finest in the world. The Southwest United States is a significant source of turquoise; Arizona, California (San Bernardino, Imperial, and Inyo counties), Colorado (Conejos, El Paso, Lake, and Saguache counties), New Mexico (Eddy, Grant, Otero, and Santa Fe counties) and Nevada (Clark, Elko, Esmerelda County, Eureka, Lander, Mineral County and Nye counties) are (or were) especially rich. The deposits of California and New Mexico were mined by pre-Columbian Native Americans using stone tools, some local and some from as far away as central Mexico. Cerrillos, New Mexico is thought to be the location of the oldest mines; prior to the 1920s, the state was the country's largest producer; it is more or less exhausted today. Only one mine in California, located at Apache Canyon, operates at a commercial capacity today.
The turquoise occurs as vein or seam fillings, and as compact nuggets; these are mostly small in size. While quite fine material—rivalling Iranian material in both color and durability—is sometimes found, most American turquoise is of a low grade (called "chalk turquoise"); high iron levels mean greens and yellows predominate, and a typically friable consistency precludes use in jewelry in the turquoise's untreated state. Arizona is currently the most important producer of turquoise by value, with the vivid Bisbee Blue being a good example of the state's natural endowment; much of the Arizona material is recovered as a byproduct of copper mining.
Nevada is the country's other major producer, with more than 120 mines which have yielded significant quantities of turquoise. Unlike elsewhere in the US, most Nevada mines have been worked primarily for their gem turquoise and very little has been recovered as a byproduct of other mining operations. Nevada turquoise is found as nuggets, fracture fillings and in breccias as the cement filling interstices between fragments. Because of the geology of the Nevada deposits, a majority of the material produced is hard and dense, being of sufficient quality that no treatment or enhancement is required. While nearly every county in the state has yielded some turquoise, the chief producers are in Lander and Esmerelda Counties. Most of the turquoise deposits in Nevada occur along a wide belt of tectonic activity that coincides with the state's zone of thrust faulting. It strikes about N15E and extends from the northern part of Elko County, southward down to the California border southwest of Tonopah. Nevada has produced a wide diversity of colors and mixes of different matrix patterns, with turquoise from Nevada coming in various shades of blue, blue-green, and green. Nevada produces some unique shades of bright mint to apple to neon yellow green. Some of this unusually colored turquoise may contain significant zinc and iron, which is the cause of the beautiful bright green to yellow-green shades. Some of the green to green yellow shades may actually be Variscite or Faustite, which are secondary phosphate minerals similar in appearance to turquoise. A significant portion of the Nevada material is also noted for its often attractive brown or black limonite veining, producing what is called "spiderweb matrix". While a number of the Nevada deposits were first worked by Native Americans, the total Nevada turquoise production since the 1870s has been an estimated at more than 600 tons, including nearly 400 tons from the Carico Lake mine. In spite of increased costs, small scale mining operations continue at a number of turquoise properties in Nevada, including the Godber, Orvil Jack and Carico Lake Mines in Lander County, the Pilot Mountain Mine in Mineral County, and several properties in the Royston and Candelaria areas of Esmerelda County.
Rough nuggets from the McGuinness Mine, Austin; Blue and green cabochons showing spiderweb, Bunker Hill Mine, RoystonIn 1912, the first deposit of distinct, single-crystal turquoise was discovered in Lynch Station, Campbell County, Virginia. The crystals, forming a druse over the mother rock, are very small; 1 mm (0.04 inches) is considered large. Until the 1980s Virginia was widely thought to be the only source of distinct crystals; there are now at least 27 other localities. The specimens are highly valued by collectors.
In an attempt to recoup profits and meet demand, some American turquoise is treated or enhanced to a certain degree. These treatments include innocuous waxing and more controversial procedures, such as dyeing and impregnation (see Treatments). There are however, some American mines which produce materials of high enough quality that no treatment or alterations are required. Any such treatments which have been performed should be disclosed to the buyer on sale of the material.
Other sources
China has been a minor source of turquoise for 3,000 years or more. Gem-quality material, in the form of compact nodules, is found in the fractured, silicified limestone of Yunxian and Zhushan, Hubei province. Additionally, Marco Polo reported turquoise found in present-day Sichuan. Most Chinese material is exported, but a few carvings worked in a manner similar to jade exist. In Tibet, where green turquoise has long been appreciated, gem-quality deposits purportedly exist in the mountains of Derge and Nagari-Khorsum in the east and west of the region respectively. However, the existence of these deposits lacks corroboration.
Other notable localities include: Afghanistan; Australia (Victoria and Queensland); northern Chile (Chuquicamata); Cornwall; Saxony; Silesia; and Turkestan.
History of use
Trade in turquoise crafts, such as this freeform pendant dating from 1000–1040 CE, is believed to have brought the Ancestral Puebloans of the Chaco Canyon great wealth. The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of Ancient Egypt, the Aztecs (and possibly other Pre-Columbian Mesoamericans), Persia, Mesopotamia, the Indus Valley, and to some extent in ancient China since at least the Shang Dynasty.[8] Despite being one of the oldest gems, probably first introduced to Europe (through Turkey) with other Silk Road novelties, turquoise did not become important as an ornamental stone in the West until the 14th century, following a decline in the Roman Catholic Church's influence which allowed the use of turquoise in secular Jewelry. It was apparently unknown in India until the Muhgal period, and unknown in Japan until the 18th century. A common belief shared by many of these civilizations held that turquoise possessed certain prophylactic qualities; it was thought to change color with the wearer's health and protect him or her from untoward forces.
The Aztecs inlaid turquoise, together with gold, quartz, malachite, jet, jade, coral, and shells, into provocative (and presumably ceremonial) mosaic objects such as masks (some with a human skull as their base), knives, and shields. Natural resins, bitumen and wax were used to bond the turquoise to the objects' base material; this was usually wood, but bone and shell were also used. Like the Aztecs, the Pueblo, Navajo and Apache tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the archer dead aim. Among these peoples turquoise was used in mosaic inlay, in sculptural works, and was fashioned into toroidal beads and freeform pendants. The Ancestral Puebloans (Anasazi) of the Chaco Canyon and surrounding region are believed to have prospered greatly from their production and trading of turquoise objects. The distinctive silver jewelry produced by the Navajo and other Southwestern Native American tribes today is a rather modern development, thought to date from circa 1880 as a result of European influences.
In Persia, turquoise was the de facto national stone for millennia, extensively used to decorate objects (from turbans to bridles), mosques, and other important buildings both inside and out, such as the Medresseh-I Shah Hussein Mosque of Isfahan. The Persian style and use of turquoise was later brought to India following the establishment of the Mughal Empire there, its influence seen in high purity gold Jewelry (together with ruby and diamond) and in such buildings as the Taj Mahal. Persian turquoise was often engraved with devotional words in Arabic script which was then inlaid with gold.
The iconic gold burial mask of Tutankhamun, inlaid with turquoise, lapis lazuli, carnelian and colored glass. Cabochons of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold Jewelry of Tibet and Mongolia, where a greener hue is said to be preferred. Most of the pieces made today, with turquoise usually roughly polished into irregular cabochons set simply in silver, are meant for inexpensive export to Western markets and are probably not accurate representations of the original style.
The Egyptian use of turquoise stretches back as far as the First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from Tutankhamun's tomb, most notably the Pharaoh's iconic burial mask which was liberally inlaid with the stone. It also adorned rings and great sweeping necklaces called pectorals. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a scarab motif, accompanied by carnelian, lapis lazuli, and in later pieces, colored glass. Turquoise, associated with the goddess Hathor, was so liked by the Ancient Egyptians that it became (arguably) the first gemstone to be imitated, the fair semblance created by an artificial glazed ceramic product known as faience. (A similar blue ceramic has been recovered from Bronze Age burial sites in the British Isles.)
The French conducted archaeological excavations of Egypt from the mid-19th century through the early 20th. These excavations, including that of Tutankhamun's tomb, created great public interest in the western world, subsequently influencing Jewelry, architecture, and art of the time. Turquoise, already favored for its pastel shades since c. 1810, was a staple of Egyptian Revival pieces. In contemporary Western use, turquoise is most often encountered cut en cabochon in silver rings, bracelets, often in the Native American style, or as tumbled or roughly hewn beads in chunky necklaces. Lesser material may be carved into fetishes, such as those crafted by the Zuni. While strong sky blues remain superior in value, mottled green and yellowish material is popular with artisans. In Western culture, turquoise is also the traditional birthstone for those born in the month of December.
Turquoise may have significance in Judeo-Christian scripture: In the Book of Exodus, the construction of a "breastplate of judgment" is described as part of the priestly vestments of Aaron (Exodus 28:15–30). Attached to the ephod, the breastplate was adorned with twelve gemstones set in gold and arranged in four rows, each stone engraved with the name of one of the Twelve Tribes of Israel. Of the four stones in the third row, the first and second have been translated to be turquoise by various scholars; others disagree, however, translating the stones to be jacinth (zircon) and agate respectively.[9] Scholars also disagree as to which tribes each stone is meant to represent.
Imitations
The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product faience. Later glass and enamel were also used, and in modern times more sophisticated ceramics, porcelain, plastics, and various assembled, pressed, bonded, and sintered products (composed of various copper and aluminum compounds) have been developed: examples of the latter include "Viennese turquoise", made from precipitated aluminum phosphate colored by copper oleate; and "neolith", a mixture of bayerite and copper phosphate. Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972 Pierre Gilson introduced one fairly close to a true synthetic (it does differ in chemical composition owing to a binder used, meaning it is best described as a stimulant rather than a synthetic). Gilson turquoise is made in both a uniform color and with black "spiderweb matrix" veining not unlike the natural Nevada material.
Some natural blue to blue-green materials, such as this botryoidal chrysocolla with quartz drusy, are occasionally confused with, or used to imitate turquoise. The most common imitation of turquoise encountered today is dyed howlite and magnesite, both white in their natural states, and the former also having natural (and convincing) black veining similar to that of turquoise. Dyed chalcedony, jasper, and marble is less common, and much less convincing. Other natural materials occasionally confused with or used in lieu of turquoise include: variscite; faustite; chrysocolla (especially when impregnating quartz); lazulite; smithsonite; hemimorphite; wardite; and a fossil bone or tooth called odontolite or "bone turquoise", colored blue naturally by the mineral vivianite. While rarely encountered today, odontolite was once mined in large quantities—specifically for its use as a substitute for turquoise—in southern France.
These fakes are detected by gemologists using a number of tests, relying primarily on non-destructive, close examination of surface structure under magnification; a featureless, pale blue background peppered by flecks or spots of whitish material is the typical surface appearance of natural turquoise, while manufactured imitations will appear radically different in both color (usually a uniform dark blue) and texture (usually granular or sugary). Glass and plastic will have a much greater translucency, with bubbles or flow lines often visible just below the surface. Staining between grain boundaries may be visible in dyed imitations.
Some destructive tests may, however, be necessary; for example, the application of diluted hydrochloric acid will cause the carbonates odontolite and magnesite to effervesce and howlite to turn green, while a heated probe may give rise to the acrid smell so indicative of plastic. Differences in specific gravity, refractive index, light absorption (as evident in a material's absorption spectrum), and other physical and optical properties are also considered as means of separation. Imitation turquoise is so prevalent that it likely outnumbers real turquoise by a wide margin. Even material used in authentic Native American and Tibetan Jewelry is often fake or, at best, heavily treated.
Treatments
Turquoise is treated to enhance both its color and durability (i.e., increased hardness and decreased porosity). Historically, light waxing and oiling were the first treatments to be used (since ancient times), providing a wetting effect (thereby enhancing the color and luster); this treatment is more or less acceptable by tradition, and because such material is usually of a higher grade to begin with. Conversely, the later development of pressure impregnation of otherwise unsaleable chalky American material by epoxy and plastics (such as polystyrene) and water glass—also producing a wetting effect in addition to improving durability—are rejected by some as too radical an alteration. Plastic and water glass are technologically superior to oil and wax in that the former treatment are far more permanent and stable, and can be applied to material too friable for oil or wax to be of sufficient help; such material is termed "bonded" or "stabilized" turquoise. The epoxy binding technique was first developed in the 1950s and has been attributed to Colbaugh Processing of Arizona, a company that still operates today. The majority of American material is now treated in this manner; although it is a costly process requiring many months to complete, without impregnation most American mining operations would be unprofitable.
Oiled and waxed stones are also prone to "sweating" under even gentle heat or if exposed to too much sun, and they may develop a white surface film or bloom over time. (With some skill, oil and wax treatments can be restored.) Likewise, the use of Prussian blue and other dyes—often in conjunction with bonding treatments—to enhance (that is, make uniform or completely change) color is regarded as fraudulent by purists—especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise. Perhaps the most radical of treatments is "reconstitution", wherein supposedly fragments of fine material too small to be used singly are powdered and then bonded to form a solid mass. Much (if not all) of this "reconstituted" material is likely a complete fabrication (with no natural components), or may have foreign filler material added to it (see Imitations section). Another treatment—the details of which remain undisclosed—is the so-called Zachery process, named after its developer, electrical engineer and turquoise trader James E. Zachery. This process claims to use only medium grade material at a minimum, leaving the turquoise harder and with a better color and luster.
As the finer turquoise is often found as thin seams, it may be glued to a base of stronger foreign material as a means of reinforcement. These are termed doublets and can be very deceptive in certain Jewelry setting styles (such as closed back and bevel settings). Some turquoise is cut with the mother rock serving as a base; these are usually not considered doublets but may have an intrinsic value lower than that of "whole" stones. Doublets, like the aforementioned treatments, are legal provided they are disclosed to the customer before sale.
As is so often with gems, full disclosure is frequently not given; it is therefore left to gemologists to detect these treatments in suspect stones, using a variety of testing methods—some of which are necessarily destructive. For example, the use of a heated probe applied to an inconspicuous spot will reveal oil, wax, or plastic treatment with certainty.
Valuation and care
Richness of color is the chief determiner of value in turquoise; generally speaking, the most desirable is a strong sky to "robin's egg" blue (in reference to the eggs of the American Robin); value decreases with the increase of green hue, lightening of color, and mottling. In Tibet, however, a greener blue is said to be preferred. Whatever the color, turquoise should not be excessively soft or chalky; even if treated, such lesser material (to which most turquoise belongs) is liable to fade or discolor over time and will not hold up to normal use in Jewelry.
The mother rock or matrix in which turquoise is found can often be seen as splotches or a network of brown or black veins running through the stone in a netted pattern; this veining may add value to the stone if the result is complimentary, but such a result is uncommon. Such material is sometimes described as "spiderweb matrix"; it is most valued in the Southwest United States and Far East, but is not highly appreciated in the Near East where unblemished and vein-free material is ideal (regardless of how complimentary the veining may be). Uniformity of color is desired, and in finished pieces the quality of workmanship is also a factor; this includes the quality of the polish and the symmetry of the stone. Calibrated stones—that is, stones adhering to standard Jewelry setting measurements—may also be more sought after. Like coral and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimeters rather than weight.
Turquoise is treated in many different ways, some more permanent and radical than others. Controversy exists as to whether some of these treatments should be acceptable, but one can be more or less forgiven universally: This is the light waxing or oiling applied to most gem turquoise to improve its color and luster; if the material is of high quality to begin with, very little of the wax or oil is absorbed and the turquoise therefore does not "rely" on this impermanent treatment for its beauty. All other factors being equal, untreated turquoise will always command a higher price. Bonded and "reconstituted" material is worth considerably less.
Being a phosphate mineral, turquoise is inherently fragile and sensitive to solvents; perfume and other cosmetics will attack the finish and may alter the color of turquoise gems, as will skin oils, as will most commercial jewelry cleaning fluids. Prolonged exposure to direct sunlight may also discolor or dehydrate turquoise. Care should therefore be taken when wearing such jewels: cosmetics, including sunscreen and hairspray, should be applied before putting on turquoise Jewelry, and they should not be worn to a beach or other sun-bathed environment. After use, turquoise should be gently cleaned with a soft cloth to avoid a build up of residue, and should be stored in its own box to avoid scratching by harder gems. Also, make sure the box is not airtight, or the turquoise will become ruined.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Turquoise.
History of Jewelry: Turquoise
Jewelry: Diamonds
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Diamond
Optical propertiesTuesday, June 6, 2006
Sapphires in the United States
The production of gem-quality sapphires in the United States is not new or recent. In 1865, the first U.S. sapphires were found in the gravels of the Missouri River in Lewis and Clark County, Montana. This was followed by subsequent discoveries on Dry Cottonwood Creek in Deer Lodge County in 1889, on Rock Creek in Granite County in 1892, and in Yogo Gulch in Judith Basin County in 1895. Additionally, small amounts of sapphire are recovered from Quartz Gulch in Granite County, Pole Creek in Madison County, the Missouri River in Chouteau County, and Brown's Gulch in Silver Bow County. Furthermore, corundum crystals, from which star sapphires have been cut, are found in Beaverhead and Madison Counties. Also, in 1895, the first sapphires were produced from the Cowee Valley in Macon County, North Carolina. But until very recently, with the exception of Yogo Gulch material, the commercial gemstone industry has had limited interest in U.S. sapphires.
Montana.--Mining of Yogo Gulch sapphires began within a year of their discovery in 1895 and continued for 39 years. In 1923, the mine was damaged so badly by rain that it could not economically recover. Other attempts have been made to commercially mine the deposit, but to date, all of these attempts have ended in economic failure.
Yogo's are unique among the world's sapphires. They lack the color zoning so prevalent in other sapphires, their uniform "corn-flower blue" color is natural (not the result of heat-treating), and their clarity is uniformly high. These features rank them among the world's finest sapphires. Unfortunately, the rough is both small and flat, wafer-like in shape. The majority of the crystals or pieces of crystals recovered are too small to be cut, most are less than 1 carat and finds of over 2 carats are rare. Reportedly, the largest crystal was a 19 carat stone found in 1910 that was cut into an 8-carat stone. The size of the cut stones greatly restrict the market for Yogo's, they are beautiful, small, very expensive sapphires.
Currently, Yogo sapphires are produced from three sources: Rancor lnc., produces material from the original Yogo Gulch deposit; Vortex Mining produces from a recently discovered extension of the Yogo dike; and material is produced by individuals from privately owned lots in Sapphire Village. The first two producers market only cut stones and finished goods and the third is comprised essentially of hobbyists.
Historically, the amount of sapphires produced from the Missouri River and Rock Creek areas greatly exceeded that from Yogo Gulch. However, the value of the material produced from Yogo, reported to be in excess of $30 million, is significantly greater than that of the combined values of the other areas. This relationship is rapidly changing.
The combination of large volume commercial operations on the Missouri River, and to some extent Rock Creek, plus the advent of successful heat-treating techniques for the material has greatly enhanced the acceptance of these sapphires by the gemstone industry. This enhanced acceptance has resulted in a significant increase in the market for and value of U.S. sapphires. Unconfirmed reports have circulated that a parcel of select 3- to 10-carat material, suitable for heat-treating, was sold for as much as $40,000 per kilogram. A more realistic price for 3- to 10-carat, sorted mine-run material is in the range of $5,000 per kilogram, with many kilograms of mine-run rough selling for $1,000 per kilogram.
The sapphires from the Missouri River gravels in Lewis and Clark County are a mixture of rough and pitted crystals showing well defined faces and completely rounded and smooth-surface highly stream worn pebbles. The majority of the material is pale blue or blue-green, with deep blue stones quite rare. Stones also are found in pastel blue, green, pink, pale red, purple, yellow, and orange. Most of the stones recovered are less than 6.4 millimeters in diameter, but material 6.4 to 12.7 millimeters in diameter are not uncommon. Material greater than 12.7 millimeters in diameter is rare.
Currently there are seven operations on the Missouri River that commercially produce sapphires and/or operate a dig-for-fee area. Not all of these may be active in any one year. It is the author's understanding that one operation, currently inactive, (a self-propelled floating 16-inch suction dredge) is for sale. The mines operate from about the last week of May through the first week of September.
The Rock Creek sapphires are very similar to the sapphires from the Missouri River but differ in the general shape of the crystals. The stones are basically crude hexagonal plates about the same dimension in width and height, with a much higher percentage of the material being well rounded water worn pebbles. There appears to be more of the larger sized (greater than 12.7 millimeters) material. Additionally, it is reported that the Rock Creek material has a greater percentage of stones that can be heat-treated for color enhancement.
During the past several years, there has been only a single producer on Rock Creek. The producer operated both a commercial recovery plant and a fee recovery area. The fee recovery area sold buckets of gravel for washing and also offered, for a predetermined fixed fee, the output of one day's operation of the commercial wash plant. There is work underway which would result in a second, much larger producer, opening an operation on another deposit in the area. If things go as planned, the new operation on Rock Creek would be the largest sapphire producer in Montana.
There are a number of locations between Dillon in Beaverhead County and Ennis in Madison County that produce lavender, grayish-lavender, bluish-gray, and gray hexagonal sapphire crystals that, when cut, produce stones that contain four- or six-ray stars. At least one producer from the Dillon area is currently advertising the availability of this type of material. The remainder of the sapphire deposits in Montana appear to be operated by individual hobbyists.
More should be said about the effects of heat-treating techniques on Montana sapphires, and the variety of fancy colored sapphires available. Not all Montana sapphires are suitable for heat- treating because of variations in chemical composition. Also, the sapphires from the Missouri River respond to heat-treating differently than those from Rock Creek The response to heat-treating can vary also depending upon the method (individual) used to treat the sapphires.
The yield on treatment of Missouri River sapphires is lower than for Rock Creek. It is reported that 20% to 30% of Missouri River sapphires heat-treat from deep, well saturated blue to pale, pale blue. The corresponding treatment rate for Rock Creek material is in the range of 60%. Heat-treating also yields or improves the color of fancy colored sapphires. Bright yellows and oranges are the result of heat-treating, whereas heat-treating improves the color of some pinks by removing colors that can interfere with the desirable pink shades. Montana sapphires can be diffusion treated, but because of their high iron content they are not particularly well suited for this form of enhancement.
North Carolina.--North Carolina is well known for its hobbyist production of sapphire. Sapphire have been produced from the Cowee Valley in Macon County since 1895 when the American Prospecting and Mining Co. systematically mined and washed the gravels of Cowee Creek. Today a number of dig-for-fee operations are located in the Cowee Valley. Each year many people pay to dig or purchase buckets of gravel to wash in hopes of finding a sapphire, garnets, and other gem materials. Many of the dig-for-fee operations have enriched the gravels with gem materials from other locations.
Every year articles appear in magazines and newspapers about large and valuable sapphires found at one or more of the mines in Cowee Valley. No doubt large corundum crystals and pieces of corundum are found each year. By the same token, valuable sapphires may be found, but the number of large valuable gemstones are far less than reported, and the values are generally not as great as reported. During the period when the area was commercially mined, gem material was found that would cut fine quality 3- to 4-carat stones, but the amount of quality gem material available has greatly declined. It is doubtful that North Carolina will ever again boast of commercial sapphire production, or that the commercial gemstone industry will seriously consider the State's sapphire deposits.
Monday, June 5, 2006
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical formula is ZrSiO4. Hafnium is almost always present ranging from 1 to 4%. The crystal structure of zircon is tetragonal crystal class. The natural color of zircon varies between colorless, yellow-golden, red, brown or green. Colorless specimens that show gem quality are a popular substitute for diamond; these specimens are also known as "Matura diamond" (but note that cubic zirconia is a completely different synthetic mineral with a different chemical composition).
Zircon is a remarkable mineral, if only for its almost ubiquitous presence in the crust of Earth. It is found in igneous rocks (as primary crystallization products), in metamorphic rocks (as recrystallized grains) and in sedimentary rocks (as detrital grains). Large zircon crystals are seldom abundant. Their average size, e.g. in granite rocks, is about 100-300 µm, but they can also grow to sizes of several centimeters, especially in pegmatites.
The pervasive occurrence of zircon has become more important since the discovery of radiometric dating. Zircons contain amounts of uranium and thorium (from 10 ppm up to 5 wt%) and can be dated using modern analytical techniques. Since zircons have the capability to survive geologic processes like erosion, transport, even high-grade metamorphism, they are used as protolith indicators. The oldest minerals found so far are zircons from the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, with an age of 4.404 billion years. This age is interpreted to be the age of crystallization. These zircons are not only the oldest minerals on earth, they also show another interesting feature. Their oxygen isotopic composition has been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth. This is a spectacular interpretation that has been published in top scientific journals but is widely disputed. It is most likely that the oxygen isotopes, and other compositional features (the rare earth elements), simply record hydrothermal alteration. The timing of the alteration is uncertain, but this negates the necessity for ancient liquid-water oceans.
Owing to their uranium and thorium content, some zircons may undergo metamictization. This partially disrupts the crystal structure and explains the highly variable properties of zircon.
Commercially, zircons are mined for the metal zirconium which is used for abrasive and insolating purposes. It is the source of zirconium oxide , one of the most refractory materials known. Crucibles of ZrO are used to fuse platinum at temperatures in excess of 1755 oC. Zirconium metal is used in nuclear reactors due to its neutron absorption properties. Large specimens are appreciated as gemstones, owing to their high refractive index (zicon has a refraction of around 1.95, diamond of around 2.4). The color of zircons that do not have gem quality can be changed by heat treatment. Depending on the amount of heat applied, colorless, blue and golden-yellow zircons can be made.
The name derives from the Arabic word zarqun, meaning vermilion, or perhaps from the Persian zargun, meaning golden-colored. These words are corrupted into "jargoon", a term applied to light-colored zircons. Yellow zircon is called hyacinth, from a word of East Indian origin; in the Middle Ages all yellow stones of East Indian origin were called hyacinth, but today this term is restricted to the yellow zircons.
Zircon is a common accessory mineral and found worldwide. Noted occurrences include: in the Ural Mountains; Trentino, Monte Somma; and Vesuvius, Italy; Arendal, Norway; Sri Lanka, India; Thailand; at the Kimberley mines, Republic of South Africa; Madagascar; and in Canada in Renfrew County, Ontario, and Grenville, Quebec. In the United States: Litchfield, Maine; Chesterfield, Massachusetts; in Essex, Orange, and St. Lawrence Counties, New York; Henderson County, North Carolina; the Pikes Peak district of Colorado; and Llano County, Texas.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Zircon.
History of Jewelry: Zircon
Monday, May 1, 2006
Jewelry: Troy Ounce
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Troy weight is a system of units of mass customarily used for precious metals and gemstones
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia Troy Ounce.
History of Jewelry: Troy Ounce
Tuesday, March 28, 2006
History of the Star of David
The Star of David is a poplar theme for Jewish Jewelry.
The six points of the Star of David symbolize God's rule over the universe in all six directions: north, south, east, west, up and down.
Originally, the Hebrew name Magen David -- literally "Shield of David" -- poetically referred to God. It acknowledges that our military hero, King David, did not win by his own might, but by the support of the Almighty. This is also alluded to in the third blessing after the Haftorah reading on Shabbat: "Blessed are you God, Shield of David."
The Star of David (Magen David in Hebrew or Mogen Dovid in Ashkenazi Hebrew, Shield of David, Solomon's Seal, or Seal of Solomon) is a generally recognized symbol of Judaism and Jewish identity. Geometrically it is a hexagram. It is also known colloquially as the Jewish Star. With the establishment of the State of Israel the Jewish Star on the flag of Israel has also become a symbol of Israel.
Origin
The shield of David is not mentioned in rabbinic literature. Notably, not a single archeological proof exists as yet concerning the use of this symbol in the Holy Land in ancient times, even after King David. A David's shield has recently been noted on a Jewish tombstone at Taranto, in Southern Italy, which may date as early as the third century of the common era. The earliest Jewish literary source which mentions it, the Eshkol ha-Kofer of the Karaite Judah Hadassi (middle of the 12th century), says, in ch. 242: "Seven names of angels precede the mezuzah: Michael, Gabriel, etc.... Tetragrammaton protect thee! And likewise the sign called 'David's shield' is placed beside the name of each angel." It was, therefore, at this time a sign on amulets.
In magic papyri of antiquity, pentagrams, together with stars and other signs, are frequently found on amulets bearing the Jewish names of God, and used to guard against fever and other diseases. Curiously enough, only the pentacle appears, not the hexagram. In the great magic papyrus at Paris and London there are twenty-two signs side by side, and a circle with twelve signs, but neither a pentacle nor a hexagram. The syncretism of Hellenistic, Jewish, and Coptic influences probably did not, therefore, originate the symbol. It is possible that it was the Kabbalah that derived the symbol from the Templars. Kabbalah makes use of this sign, arranging the Ten Sephiroth, or spheres, in it, and placing it on amulets.
A manuscript Tanakh dated 1307 and belonging to Rabbi Yosef bar Yehuda ben Marvas from Toledo, Spain, was decorated with a Shield of David.
In the synagogues, perhaps, it took the place of the mezuzah, and the name "shield of David" may have been given it in virtue of its presumed protective powers. The hexagram may have been employed originally also as an architectural ornament on synagogues, as it is, for example, on the cathedrals of Brandenburg and Stendal, and on the Marktkirche at Hanover. A pentacle in this form is found on the ancient synagogue at Tell Hum.
In 1354, King of Bohemia Charles IV prescribed for the Jews of Prague a red flag with both David's shield and Solomon's seal, while the red flag with which the Jews met King Matthias of Hungary in the 15th century showed two pentacles with two golden stars (Schwandtner, Scriptores Rerum Hungaricarum, ii. 148). The pentacle, therefore, may also have been used among the Jews. It occurs in a manuscript as early as the year 1073 (facsimile in M. Friedmann, Seder Eliyahu Rabbah ve-Seder Eliyahu Ztṭa, Vienna, 1901).
In 1460, the Jews of Ofen (Budapest, Hungary) received King Mathios Kuruvenus with a red flag on which were two Shields of David and two stars. In the first Hebrew prayer book, printed in Prague in 1512, a large Shield of David appears on the cover. In the colophon is written: "Each man beneath his flag according to the house of their fathers... and he will merit to bestow a bountiful gift on anyone who grasps the Shield of David." In 1592, Mordechai Maizel was allowed to affix "a flag of King David, similar to that located on the Main Synagogue" to his synagogue in Prague. In 1648, the Jews of Prague were again allowed a flag, in acknowledgment of their part in defending the city against the Swedes. On a red background was a yellow Shield of David, in the centre of which was a Swedish star.
Jewish lore links the symbol to the "Seal of Solomon", the magical signet ring used by King Solomon to control demons and spirits. Jewish lore also links the symbol to a magic shield owned by King David that protected him from enemies. Following Jewish emancipation after the French revolution, Jewish communities chose the Star of David to represent themselves, comparable to the cross used by most Christians. The star is found on the flag of Israel.
The shape of the star is an example of the hexagram, a symbol which has significance for other belief systems. The hexagram pre-dates its use by Jews. Its most prevalent usage outside of Judaism was and is the occult.
Another theory about the origin of the shape is that it is simply 2 of the 3 letters in the name David. In its Hebrew spelling, David contains only 3 characters, 2 of which are "D" (or "Dalet", in Hebrew). In ancient times, this letter was written in a form much like a triangle, similar to the greek letter "Delta", with which it shares a sound and the same (4th) position in their respective alphabets, as it does with English. The symbol may have been a simple family crest formed by flipping and juxtaposing the two most prominent letters in the name.
So whether it is a blue star waving proudly on a flag, or a gold star adorning a synagogue's entrance, the Star of David stands as a reminder that for the Jewish people... in God we trust.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Star of David.
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