LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY LAWRENCE LAWRY / SCIENCE PHOTO LIBRARY
Topaz gemstones. This silicate mineral (aluminium silicate fluoride hydroxide) can range in colour from golden brown to yellow. A blue variety is often confused with aquamarine, although it does not occur in nature. Topaz can be polished in a variety of shapes: oval (centre left), cushion cut (far right) and opposed bar (across bottom) are seen. It is rated as 8 out of 10 on the Mohs hardness scale, with diamond rated as 10.
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