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Home » Minerals » Topaz

Topaz


A very popular gemstone and the Mohs Scale mineral with a hardness of 8


What is Topaz?



Topaz is a silicate mineral most often found in igneous rocks of felsic composition. It is also found in some hydrothermal veins and the hydrothermally altered rocks that surround them. It is a common mineral of pegmatites and also found in the cavities of rhyolite and granite. Rarely, topaz is found in metamorphic rocks such as schist or quartzite. Topaz is not an abundant mineral but occurs worldwide in the types of rocks listed above.

Compared to other minerals, topaz is relatively resistant to weathering and stream abrasion. These characteristics enable it to be found in the stream sediments derived from the weathering of topaz-bearing rocks. It is sometimes produced by placer mining.


Physical Properties of Topaz

Chemical Classification silicate
Color colorless, white, yellow, amber, pink, blue, green, gray
Streak colorless - harder than the streak plate
Luster normally vitreous
Diaphaneity transparent to translucent
Cleavage perfect basal cleavage
Mohs Hardness 8
Specific Gravity 3.4 to 3.6
Diagnostic Properties hardness, prismatic crystals, sometimes striated, cleavage, specific gravity
Chemical Composition Al2SiO4(F,OH)2
Crystal System orthorhombic
Uses


Topaz Gemstones



Topaz is a very popular gemstone. Gem quality topaz most commonly occurs in nature as a colorless crystal. When cut as a gemstone these colorless specimens generally have the lowest value. A significant amount of natural topaz also occurs in a color range spanning from yellow to brown. Small amounts of natural blue and pink topaz are found but the abundance of natural stones in these colors is very low.


Treated Topaz Gemstones



Blue topaz is a very popular gemstone but this color is rarely found in nature. To produce blue topaz, some dealers irradiate clear topaz then heat it to produce a blue gemstone. The most desirable blue topaz stones have a color that resembles aquamarine. Today, most of the blue topaz being sold as a gemstone has been treated. Dealers should label these stones as "treated" or "enhanced" so that customers know the stone's history. The price of blue topaz has declined in recent years because so much blue topaz has been produced through treatment.

A small amount of topaz occurs naturally as pink and red crystals. These are the most expensive colors of natural topaz. However, brown topaz can sometimes be heat treated to produce a pink stone.

Two other colors of topaz are seen in the gemstone market. One is a green topaz that has been produced by diffusing chromium into the outer surface of the stone. Another treated stone is sold under the name "mystic" topaz. This is a stone with an iridescent appearance that is produced by vapor coating the surface of clear topaz with titanium oxide. This surface coating is not permanent and many mystic topaz gemstones quickly show signs of wear.


Synthetic Topaz



Some synthetic topaz is produced, cut and sold as gemstones. It should be clearly labeled as "laboratory", "synthetic", "created" or some other term to let the buyer know that it is not natural material. Anyone purchasing gemstones should be aware that treated and synthetic gems exist and are sometimes sold without proper labels.


Topaz Hardness and Durability



Topaz is a very hard mineral. It is used for the standard hardness of eight in the Mohs Hardness Scale. Some minerals of great hardness can be broken rather easily. Topaz has a perfect basal cleavage making it vulnerable to breakage. This cleavage makes topaz a somewhat fragile gemstone. It is best suited for pendants and earrings that receive little hard use and less suited as a ring stone that might be bumped while in use.


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blue synthetic topaz
Synthetic blue faceted topaz. 12.05 carats, 14x11 mm, Russian made.




brown topaz uncut stones
Rough brown topaz crystal sections.


pink treated topaz faceted
Faceted pink "treated" topaz. 2.4 carats, 9x7mm, from Africa.


clear topaz faceted stone
Faceted clear topaz. 6.25 carats, 14x10 mm, from Switzerland.


blue topaz faceted
Blue faceted topaz. 1.40 carats, 9x6 mm, from Brazil.


Mineral Information
 Anhydrite
 Apatite
 Arsenopyrite
 Augite
 Azurite

 Barite
 Bauxite
 Beryl
 Biotite
 Bornite

 Calcite
 Cassiterite
 Chalcocite
 Chalcopyrite
 Chlorite
 Chromite
 Chrysoberyl
 Cinnabar
 Clinozoisite
 Copper
 Cordierite
 Corundum
 Cuprite
 Diamond
 Diopside
 Dolomite

 Enstatite
 Epidote

 Fluorite

 Galena
 Garnet
 Glauconite
 Gold
 Graphite
 Gypsum

 Halite
 Hematite
 Hornblende

 Ilmenite

 Jadeite

 Kyanite
 Limonite

 Magnesite
 Magnetite
 Malachite
 Marcasite
 Molybdenite
 Monazite
 Muscovite

 Nepheline
 Nephrite

 Olivine
 Orthoclase

 Plagioclase
 Prehnite
 Pyrite
 Pyrophyllite
 Pyrrhotite

 Quartz

 Rhodochrosite
 Rhodonite
 Rutile
 Scapolite
 Serpentine
 Siderite
 Sillimanite
 Silver
 Sodalite
 Sphalerite
 Spinel
 Spodumene
 Staurolite
 Sulfur
 Sylvite

 Talc
 Titanite
 Topaz
 Tourmaline
 Turquoise

 Uraninite

 Witherite
 Wollastonite

 Zircon
 Zoisite


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