Silicates: Topaz

Composition: Al₂SiO₄(OH,F)₂

Crystal system: Orthorhombic; prismatic crystals, also massive and granular

5.30.1
cleavable blue topaz
CO USA

Properties:

• Vitreous lustre
• Variable color; colorless, white, pale blue, yellow, pink
• White streak
• Knife does not scratch (Mohs Hardness 8)
• Above average density
• One perfect cleavage
• Smooth fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Topaz occurs with quartz, cassiterite, fluorite and various silicates in pegmatite dikes, vein and replacement ore deposits associated with granitic rocks and also in heavy mineral sand and gravel deposits.

5.30.2 cleavable blue topaz CO USA	5.30.3 topaz crystal

Gem quality topaz occurs in a variety of colors.