Saturday, March 1, 2003

Jewish Jewelry - Sapphires

Sapphire

Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminum 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 aluminum 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.

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).

Also see Jewish Jewelry

Sapphires have an esteemed history. Tradition holds that the tablets containing the Ten Commandments were composed of sapphire, so strong that a hammer swung against them would be smashed to pieces.

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.

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 aluminum 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.

Top-quality sapphires are rare, Sapphires, call them gemstones of the sky though we may, lie well hidden in just a few places, and first have to be brought to light through hard work.

  • 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

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