PHYSICAL PROPERTIES

     Topaz Chemical composition: Al2SiO4(F,OH)2
     Class: nesosilicate
     Crystal system: orthorhombic; 2/m2/m2/m
     Crystal habit: commonly as euhedral prismatic crystals terminated by dipyramids, first and
     second order prisms, and basal pinacoids. Frequently with vertical striations on the prismatic
     faces. Also appears in crystalline masses.
     Twinning: twins are very rare in topaz
     Specific gravity: 3.4 - 3.6
     Index of refraction: 1.606 - 1.638
     Birefringence: weak (0.008-0.011)
     Pleochroism: weak to moderate, tones vary depending on color of specimen
     Hardness: 8
     Color: commonly colorless, also light to medium blue, yellow/orange/pink/red/violet with or
     without brown tone, brownish green, brown.
     Luster: vitreous
     Transparency: transparent to translucent
     Cleavage:perfect on {001}
     Fracture: conchoidal, brittle
     Streak: white
     Fluorescence: mild flourescence in some crystals

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                   TOPAZ BACKGROUND INFORMATION

Topaz (Al2SiO4(F,OH)2) is an aluminum fluorosilicate. It most often occurs colorless, but can occur
naturally in a variety of colors such as pale blue, yellow and brown. Much more rare are natural
color 'Imperial' topazes with orange, pink, red or violet tones. The colors in topaz are mainly the
result of color centers, which are sometimes affected to some extent by variations in the amounts of
F,OH and minor impurities present, with the exception of the pink, red and violet tones in some
topaz which are due to chromium impurities in the topaz crystal structure. Color centers are not fully
understood, but it can be said that they are created by radiation and destroyed (reversed) by heating
or in some cases by exposure to light.

These color causing 'color centers' can occur and be reversed by natural irradiation and heating
processes, resulting in the variety of colors exhibited by natural color topazes, or they can be
manipulated by artificial means. More than 99.9% of all blue topaz gems on the market today have
undergone an irradiation treatment to produce their blue color.

Some color centers in topaz are stable until heated hundreds of degrees while others are very
unstable, fading within a few days merely by exposure to sunlight. The natural color of the yellow to
'sherry'-colored to brown topaz crystals from the Thomas Range in Utah, USA often exhibit this 'fast
fading' phenomenon. Yellow to 'sherry'-colored to brown topaz crystals from some other locations
do not fade when exposed to sunlight, indicating a light stable color center.

Much colorless topaz becomes a brownish-green color when irradiated. Subsequent exposure to
light or heat will usually cause the brown portion of the color to fade leaving a blue color that is
stable to light. Additional heating will cause this blue color to fade and the topaz will become
colorless once again.

Some brown topazes that contain chromium impurities will become pink to violet upon heating.
These colors are stable to light and this process can be reversed by subsequent irradition.
 
 

                OCCURRENCE AND DIAGNOSTIC FEATURES

Topaz is thought to form from fluorine bearing gases given off during the later stages of solidification
in acidic igneous rocks, occuring in cavities and fissures within rhyolites and granites, and also in
granitic pegmatites where it is commonly associated with quartz, microcline, muscovite, tourmaline,
beryl and apatite.

Topaz occurs in metamorphic rocks by fluorine metasomatism in greisens and quartzites associated
with fluorite, zinnwaldite, corundum and rutile. It also occurs (rarely) in schists.

Topaz appears in hypothermal ore deposits associated with cassiterite, hematite, wolframite and
gold.

Due to topaz's hardness, it is often found in eluvial and alluvial deposits.

Topaz is characterized by its high specific gravity, hardness, crystal habit and cleavage.
 
 

                   HISTORICAL INFORMATION AND USES

The name 'topaz' was used to refer to any yellow stone in ancient times. Topaz was first used to
describe the mineral that we know today as topaz in 1747 when Henckel described the Saxony
deposits. Even today one often encounters the erronious terms smoky topaz and madeira topaz
being used for smoky quartz and citrine quartz, respectively. Until the 18th century, the name topaz
was often used in refering to our present day mineral peridot.
The name 'topaz' is thought by many to be derived from the ancient Sanskrit word tapas meaning
fire. Another theory which was first put forth by Pliny in the first century A.D. is that the name topaz
was derived from the Greek word topazos or topazion meaning to seek, which was the name of an
island in the Red Sea (known today as 'Zeberget', or the 'Island of St. John') which is thought to
have been an ancient source for the gem peridot, but not topaz.
The term imperial topaz originated in Russia in the 19th century, when topazes with pink tones were
discovered there and proclaimed by the Czar to belong only to himself and the royal family, and
others to whom he had given it as a gift.

Topaz was one of the stones in the 'Breastplate of Judgement' of Aaron, described in the bible
(Exodus: xxviii, 15-30). In Vedic astrology ( 1000's of years older than western astrology, and still
practiced by millions today), topaz is asigned to the planet jupiter. Historically, topaz has been
thought to give long life, good looks and inteligence. It is also thought to given protection from
poison, disease and sorcery.

Topaz is used as a gemstone. Its perfect cleavage makes it susceptible to being damaged if struck
upon a hard surface.

The astrological sign of topaz is Sagittarius.
Topaz is the symbolic gemstone for the 16th wedding anniversary.