Topaz

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The name Topaz is believed to be from the Greek "topazios" the ancient name of St. John's Island in the Red Sea where it was first mined. Alternatively, the name may be related to the Sanskrit word "tapas" meaning fire, alluding to the brilliance of the gem-quality material. Topaz has been known from antiquity.

ï Mineral: Topaz

ï Chemistry: Al₂(SiO₄)(F,OH)₂

ï Class: Orthosilicate

ï Crystal system: Orthorhombic

ï Color: Colorless, white, pale blue, light green, yellow, yellowish brown, or red

ï Refractive index: 1.606 – 1.644

ï Luster: Vitreous

ï Specific gravity: 3.4-3.6

ï Mohs Hardness: 8

ï Streak: Colorless (harder than streak plate)

ï Cleavage: Perfect basal cleavage

ï Fracture: Irregular/uneven, sub-conchoidal

Topaz is allochromatic, which means that its color is caused by impurity elements or defects in its crystal structure rather than by an element of its basic chemical composition. The element chromium causes natural pink, red, and violet-to-purple colors in topaz. Imperfections at the atomic level in topaz crystal structure can cause yellow, brown, and blue color. Topaz is also pleochroic, meaning that the gem can show different colors in different crystal directions

Fluorine gas in concentrations high enough to form Topaz only occurs in a few geologic environments. Topaz occurs in granitic pegmatites, high-temperature quartz veins, and vapor cavities in rhyolites. The fluorine in its composition is a limiting factor on its formation.

The primary use of topaz is as a gemstone and as a Moh's hardness index mineral (Moh's hardness of 8). Topaz is one of the hardest naturally occurring minerals and is the hardest of any silicate mineral. Precious (imperial) topaz is a birthstone for November and blue topaz is a birthstone for December. Blue topaz is the gem of the 4th anniversary and Imperial topaz is the gem of the 23rd anniversary.

Some of the locales from which specimens of Topaz are available at Taos Rockers are:

Utah (state gemstone)

Colorado

Namibia

Pakistan

Mexico

Brazil (the largest producer)

When allowed to grow unrestricted, topaz forms orthorhombic crystals, often with striations that parallel the long axis of the crystal. It also has a distinct basal cleavage that breaks perpendicular to the long axis of the crystal. This cleavage makes topaz a more fragile gemstone than its hardness of 8 would imply.

Natural blue topaz is extremely rare and is usually pale blue. Almost all of the blue topaz offered in stores today is colorless topaz that has been irradiated and then heated to produce a blue color. "Swiss blue" and "London blue" are trade names for two of the most common varieties of treated blue topaz seen in today's market.

Imperial topaz is yellow, pink (rare, if natural) or pink-orange.

Natural pink to purple topaz is also extremely rare, but these colors can also be produced in a laboratory.

Some topaz is coated with a metallic oxide that gives the stone a multicolored iridescent luster. These stones, known as "mystic topaz," appear to change color if the observer moves the stone under a light or changes the angle of observation. These coatings are also thin and can be worn through during wear.

Melody, in her book Love Is In The Earth, says “Topaz is known as a “stone of true love and success in all endeavors”…This mineral helps one to understand both the actions occurring in the “big picture” and the interrelationships occurring in the minute detail which comprise the “big picture”.”