Gem Minerals
Topaz
What it is
An aluminum fluorine silicate prized for its hardness (Mohs 8) and brilliance. Imperial topaz from Brazil displays a rare golden-orange to pink color caused by chromium. Most blue topaz on the market is irradiated and heat-treated.
How it forms
Crystallizes in fluorine-rich granite pegmatites and rhyolite cavities. Fluorine gas is the key ingredient — it's released during the final stages of granitic magma cooling.
Al₂SiO₄(F,OH)₂
