TOPAZ MINERAL FACTS Nevada Turquoise gem stones
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Topaz Mineral Facts:

Chemical Formula: Al2(F,OH)2SiO4 
The mineral has a varying composition, with variable portions of Fluorine and hydroxide ions.

Colors: The mineral is colorless, honey yellow, yellowish red, rose and rarely bluish.
On prolonged exposure the sunlight many of the color varieties eventually fade. Streak is colorless or white.

Hardness: 8

Density: 3.52 to 3.57

Cleavage:  Perfect parallel to the basal plane {001}.

Crystallography: Orthorhombic
Occurs in prismatic crystals terminated by pyramids, domes and basal plane. Often highly modified and with prism faces often vertically striated. They are notable for the number of forms that have been observed on them, especially in the prismatic zone and among the brachypyramids.

Luster:. Vitreous luster, transparent to translucent.

Optics: (Refractive Index): = 01=1.6294, 18=1.6308,
Variable, depending on relative F to OH abundance.

Imperial topaz crystal


Composition, Structure and Associated Minerals:
Topaz occurs in igneous rocks, granites, rhyolites, etc., and good crystals are found projecting into the druses, as in the Mourne Mountain granite, and in the lithophysal cavities of rhyolites, as in Colorado. It is also a mineral which occurs in tin-bearing pegmatites and in tin veins generally, formed through the agency of fluorine bearing pneumatolytic fluid vapors given off during the last stages of the solidification of igneous rocks. In these environments it is found in cavities in rhyolite lavas and granite associated with related minerals including fluorite, cassiterite, and tourmaline, apatite, etc. Topaz is also found associated in pegmatites with quartz, mica, feldspar. Because it is highly durable and hard, it is found at times in alluvial deposits as water rolled pebbles in stream sands.

Identification and Diagnostics
Recognized chiefly by its crystal forms, its basal cleavage, its unusual hardness of 8, and it's high specific gravity. The mineral is distinguished from yellow quartz by its crystallization, its greater hardness and its easy cleavage.
Topaz is infusible before the blowpipe and is insoluble in acids. The powdered mineral, when heated, moistened with cobalt nitrate and reheated, assumes a blue color, due to aluminum. Fused with microcosmic salt, gives off silicon fluoride, which etches the glass.  At a high temperature it loses its fluorine as silicon and aluminum fluorides. The mineral also can exhibit pyroelectrical properties, but these are apparently distributed without regularity in different crystals. Many crystals contain inclusions of fluids containing bubbles, and sometimes of two immiscible fluids which are normally gaseous carbon-dioxide and  liquid water.

Occurrence, Localities and Origins:
The mineral occurs principally in pegmatites, in gneisses, and in acid volcanic rocks. In all cases it is probably the result of the escape of fluorine-bearing liquids and gases emanating from cooling igneous magmas. Topaz is found in handsome crystals at Schneckenstein in Saxony, in a breccia made up of fragments of a tourmaline-quartz rock cemented by topaz. It occurs also in the pegmatites of the tin mines in Ehrenfriedersdorf, Marienberg and other places in Saxony, Bohemia, England, etc.; on the walls of cavities in a coarse granite in Jekaterinburg and the Ilmengebirge, Russia; in pale blue crystals from Adunchilon and Mursinka in  Siberia, the Mino Province, Japan; in veins of kaolin cutting a talc schist in Minas Geraes in Brazil; and in the cassitefite-bearing sands at San Luis Potosi, Durango and other points in Mexico. Imperial topaz is  the rarest and most desirable gem topaz variety, with its shades peach, pink, orange or champagne colors. Most production comes from the mines of Ouro Preto in Minas Gerais, Brazil, but the first deposits were found in the Ural Mountains of Russia. It is named for the Imperial Russian Monarchy. Some pale pink topaz comes from Afghanistan. In the United States it occurs on the walls of cavities in acid volcanic rocks, at Nathrop, Colo., in the Thomas Range, Utah, and other places. It occurs also in veins with muscovite, fluorite, diaspore and other minerals at Stoneham, Maine, and Trumbull, Conn. Blue Crystals are found in Mason County Texas. It is found associated with amazonite feldspar at a location near Hawthorne, Nevada and in the Pike's peak area of Colorado. 

The principal use of topaz is as a gemstone, though large and showy specimens are also prized by mineral collectors. Some very large crystals are occasionally available that are capable of producing gems more than two thousand carats in weight. Because of its toughness and hardness, it makes for an excellent gem for daily wear. Historically, a number of other inferior stones like quartz were once also frequently called topaz. Trade laws have outlawed this old practice. The color of the stones varies, being colorless, wine-yellow, golden brown, pale blue and pink. Most of blue colored material seen in jewelry stores is colorless material that has been irradiated. Irradiation produces colors ranging from sky to deep blues. The material has no long term radioactivity, and there are testing procedures to make sure the gems are safe.  The pink color is usually artificial, being produced by gently heating the deep orange yellow imperial colored stones. The color change is permanent, however.

For more information on this gem, see:  Topaz - The many colored Gem

Return to the Mineral Collectors Information Page

Natural Topaz

Large Topaz crystal

Topaz crystal

Brazil blue topaz

Utah topaz crystal



Please note that the author, Chris Ralph, retains all copyrights to this entire document and it may not be reproduced, quoted or copied without permission.

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