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Chemical Formula | Al2SiO4(F,OH)2 | ||||||||||
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Composition | Aluminum fluoro-hydroxyl-silicate | ||||||||||
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Color | Colorless, white, yellow, orange, brown, pink, light purple, gray, light blue, greenish blue, green | ||||||||||
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Streak | Colorless | ||||||||||
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Hardness | 8 | ||||||||||
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Crystal Forms and Aggregates |
(Orthorhombic) Prismatic, tabular, and stubby crystals, usually striated and sometimes quite large. Crystals may
contain numerous faces. Also occurs columnar, massive, grainy, and as rounded, waterworn pebbles. It may also be in the form of the Feldspar minerals, since it frequently pseudomorphs them. |
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Transparency | Transparent to translucent | ||||||||||
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Specific Gravity | 3.4 - 3.6 | ||||||||||
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Luster | Vitreous | ||||||||||
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Cleavage | 1,3 - basal | ||||||||||
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Fracture | Subconchoidal | ||||||||||
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Tenacity | Brittle | ||||||||||
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Other Names | Precious Topaz | ||||||||||
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Varieties | Citrine (a yellow-brown variety of Quartz) closely resembles yellow-brown
Topaz. Unfortunately, unscrupulous dealers have adapted
false name for Citrine so the unaware buyer thinks he is
buying the more valuable Topaz. Any "Topaz"
labeled with a prefix name (such as Gold Topaz, Madeira
Topaz, False Topaz, Brazilian Topaz, Bahia Topaz, and
Citrine Topaz) is heat-treated Citrine. However, there
are three exceptions: Imperial Topaz Oriental Topaz Precious TopazImperial Topaz is a lustrous orange-yellow to orange-brown variety of Topaz and is its most valuable gem form. Oriental Topaz is yellow to yellow-brown Sapphire Precious Topaz is used to distinguish Topaz from all other yellow to brown gems, since in ancient times the word Topaz was used for all gems of this color. Smoky Topaz is also a false name for Topaz. It is used by unscrupulous dealers to describe Smoky Quartz. Hyacinth is an orange-yellow to yellow-brown variety of Topaz. Although the name Hyacinth usually is used to describe a gem variety of Zircon of that color, it is occasionally used for Topaz as well (usually in old manuscripts). Pycnite is a columnar variety of Topaz. It may also refer to a yellow-white variety Gem varieties of Topaz are: Imperial Topaz Pink Topaz Blue Topaz Silver Topaz (colorless) Brown Topaz Green Topaz |
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In Group | Silicates ; Nesosilicates | ||||||||||
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All About | Topaz occurs naturally in many colors, but
rarely as pink and purple. Almost all pink and purple
Topaz are yellow to brown stones that were heat-treated. Topaz from certain localities may
turn colorless upon heating. Much of the deep blue Topaz
on the market is heat-treated from colorless or white
stones. The color of some Topaz specimens, namely those from Siberia, fade upon prolonged exposure to light. Such specimens should be stored in dark areas, and one should make sure not to buy a Topaz gem unless convinced that it won't fade. Topaz crystals in a matrix are rare and very much desired, since the perfect basal cleavage of Topaz causes it to separate from its base and form loose crystals. Precautions must be taken not to damage specimens, for pressure or improper faceting can cause a crystal to cleave and become ruined. |
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Uses | Topaz is a popular gemstone. All colors are
fashioned into gemstones, and the yellow-brown
("Imperial") and pink varieties are the most
valuable. Crystals, especially those still in a matrix, are greatly sought by mineral collectors. See the gemstone section on topaz |
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Striking Features | Great hardness and perfect basal cleavage | ||||||||||
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Complex Tests | Insoluble in acids | ||||||||||
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Popularity (1-4) | 1 | ||||||||||
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Prevalence (1-3) | 2 | ||||||||||
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Demand (1-3) | 1 | ||||||||||
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Distinguishing Similar Minerals |
Quartz - slightly softer (7), lacks
cleavage Chrysoberyl - lacks cleavage Beryl - lacks cleavage Apatite - softer (5) Euclase - different cleavage, otherwise hard to distinguish Fluorite - much softer (4) |
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Commonly Occurs With |
Quartz, Feldspars, Tourmaline, Beryl, Euclase, Fluorite, Garnet, Rutile, Cassiterite, Pyrophyllite | ||||||||||
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Noteworthy Localities |
The main commercial Topaz deposits are in
Ouero Prito, Minas Gerais, Brazil. Huge, transparent,
gem-quality crystals are found there. Much gem Topaz has
also come from Russia, in the Ural Mountains and Siberia.
Excellent Topaz crystals were also found in San Luis
Potosi, Mexico. In the U.S., fine colorless and blue crystals come from Mason Co., Texas (near Streeter, Katemcy, and Grit). Much gem material has also been found in the Pikes Peak area (Colorado), particularly in Glen Cove, Devils Head, and Crystal Peak. Golden brown, lustrous crystals are found in the Thomas Range, Juab Co., Utah. Small amounts of Topaz have also come from the Little Three mine, Ramona, San Diego Co., California; the Champion mine, White Mountains, Mono Co., California; Amelia Court House, Amelia Co., Virginia; Trumbull, Fairfield Co., Connecticut; Conway, Caroll Co., New Hampshire; and the Ruggles Mine, Grafton Co., New Hampshire. |
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Picture Icon Links |
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Picture Links | 1. Orthorhombic
Topaz crystals 2. Orange Topaz crystal 3. Various Topaz specimens 4. Topaz crystals on matrix 5. Rounded, waterworn, blue Topaz |
