Topaz
Classified as a gem in the group of Semi-Precious Gemstones. It has a wide variety of colors. The most expensive and hardest to find topaz is a reddish-orange topaz, Also known as 'Imperial Topaz'.
The other colors popular are dark blue.
Chemical Formula
Mohs Hardness
Specific Gravity
Crystal System
Refractive Index
Birefringence
Optical Character
Color
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Al F SiO
8
3.53
Orthorhombic
1.619 - 1.627
0.008 to 0.011
DR Biaxial (+)
Colorless, Yellow, Yellow-brown, Red-brown, Blue, Green, Pink, Red, Violoet.
2
2
4
Blue Topaz Color Chart
The blue color of topaz can be divided into 4 shades: Sky Blue Topaz,
Baby Swiss Topaz, Swiss Blue Topaz และ London Blue Topaz
Baby Swiss
Swiss Blue
London Blue
Sky Blue
Enhancement
In most cases, topaz is treatment with Irradiation
and Heat Treatment to make the color more beautiful.
Origin of Topaz
The familiar color of most topaz, ranging from colorless through to dark orange
and pale yellow, results from the activity of color center.
Blue topaz in Nature is attractive but generally pale; the dark blue stones
now familiar in jewelry have been artificially irradiated.
colorless material when irradiated gives unstable
yellow or brown color center/stable brown or blue color center.
The sources where topaz is found include:
Brazil
Brazil has been the world's most important source of topaz for decades. Almost all of the world's fine-quality imperial topaz is produced in the state of Minas Gerais in southeastern Brazil. The Ouro Preto and Capao mines have been the most important sources of yellow, orange, pink, red and violet topaz crystals for the gem and mineral specimen markets. Brazil is also the leading producer of colorless topaz, much of which is heat treated and irradiated to produce the colors of
Swiss blue and London blue.
Pakistan
The topaz is found in one of two hills that rise abruptly from the fertile agricultural plain of the Mardan District in the neighborhood of a small village. Topaz was first discovered at Ghundao in the fall of 1972 by local residents who dug the crystals secretly and then brought them to the market in Peshawar. In addition to the relatively recent discovery of significant amounts of emerald, aquamarine, and ruby, Pakistan has also begun to produce fine gem-quality pink topaz. In a small hillock of recrystallized limestone north of Katlang, narrow calcite veins encase pink topaz crystals up to 3 cm long accompanied by larger amounts of reddish brown, tan, and colorless topaz crystals.
Australia
Topaz crystals, usually colorless to pale blue, are found at a number of sites in Australia, with the finest gem material coming from Oban in New South Wales, Mt Surprise in Queensland and Flinders Island in Tasmania. In New South Wales, the Oban and Mitchell Rivers in the New England area have yielded quantities of fine topaz. It occurs as waterworn crystals, cleavage fragments and pebbles. Many large, clear gemstones have been faceted from this material.