Topaz
Silicate · Al₂SiO₄(F,OH)₂
Topaz is an aluminium silicate of hardness 8, forming glassy prismatic crystals with one perfect cleavage, in colourless, blue, golden and pink.
What is topaz?
Topaz is a hard aluminium silicate that forms glassy prismatic crystals, often with a lozenge-shaped cross-section. It occurs colourless, sky-blue, golden, pink and the prized orange-pink “imperial” topaz. Its one perfect cleavage means gem cutters must orient it carefully. Much blue topaz on the market is irradiated colourless material.
Properties
- Chemical formula
- Al₂SiO₄(F,OH)₂
- Category
- Silicate
- Hardness (Mohs)
- 8
- Crystal system
- Orthorhombic
- Lustre
- Vitreous
- Streak
- White
- Colour
- Colourless, blue, yellow, pink, “imperial” orange
- Cleavage / fracture
- Perfect basal (one direction)
How to identify topaz
- →Hardness 8: scratches quartz easily.
- →One perfect basal cleavage (breaks flat across the crystal).
- →Prismatic crystals, often with striations along the length.
- →Higher density than quartz; glassy lustre.
Where topaz is found
Topaz comes from Brazil (imperial topaz from Ouro Preto), Pakistan, Russia (the Urals) and the USA (Utah, Texas).
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