Geology Home Page physical geology historical geology planetary gems
Roger Weller, geology instructor
by KaMari Craft
Have you ever wondered what your birthstone was ? What different birthstones there were in this world ? Well I have always wondered that . My birthstone happens to be topaz . Topaz , also known as citrine can be a yellowish , orange color , or it can come in a beautiful blue color . Topaz is a silicate mineral .
chemical formula : Al2SiO4(F,OH)2
Strunz classification : 9.AF.35
crystal symmetry: Orthohombric dipyramidal
H-M symbol: (2/m 2/m 2/m)
Space group: Pbnm
Unit Cell : a=4.65 A, b = 8.8 A,
c=8.4 A , Z=4
colorless (if no impurities) , blue, brown , orange , gray , yellow, green , pink and reddish pink.
Crystal Habbit: Prismatic crystals with faces striated parallel to long dimension; also columnar, compact , massive .
Crystal system: Orthorhombic
Cleavage:  Perfect
Fracture: Subconchoidal to uneven
Mohs scale (hardness) : 8 ( defining mineral)
Luster : Vitreous
Specific gravity: 3.49-3.57
Optical properties: Biaxial(+)
Topaz of any type is a good jewelry stone and is historically one of the most important gemstones. With its relatively high refractive index and hardness of eight (Mohs scale) , with no special sensitivity to chemicals it can be used , with appropriate care (should be protected from hard knocks) , in any jewelry application . Topaz comes in many colors including clear , brown , yellow , orange , red , pink, and blue . The blue topaz , with a pale to medium blue color created by irradiation , can be found in very large sizes at affordable prices . the fine golden-yellow variety , known as Imperial Topaz , is relatively scarce. Topaz colors are rarely vivid . The most common color is yellow with red tint ; the most valuable pink to reddish . The coloring agents are iron and chromium .
The name Topaz is most probably derived from an island in the Red Sea , " Topazos " , today called Zabargad , the ancient source of peridot . In former times , all golden-brown and sometimes also green gemstones were called topaz , which caused sufficient confusion such that today real topaz is referred to as precious topaz .
Topaz is the birthstone for those who are born in the month of November .
golden topaz- photo courtesy of R.Weller/Cochise College
imperial topaz- photo courtesy of R.Weller/Cochise College
blue topaz pendant- photo courtesy of R.Weller/Cochise College
FOLKLORE , LEGENDS, AND HEALING PROPERTIES
During the Middle Ages , topaz was thought to heal both physical and mental disorders and prevent death . The Greeks believed it had power to increase strength and to make its wearer invisible while the Romans believed it had power to improve eyesight . The Egyptians wore it as an amulet to protect them from injury .