Topaz Identification Sheet

The Mohs 8 reference mineral: hard enough to scratch quartz, with perfect basal cleavage and striated prismatic crystals.

Rock type: Igneous, Hydrothermal

For: Collectors, Lapidary Artists

Mohs hardness 8 8 (defines the scale point)

Streak Colorless, White Colorless to white

Luster Vitreous

CleavagePerfect basal {001}

Crystal habit Prismatic, Columnar, Granular, Massive Prismatic crystals, often columnar; also granular and massive

Topaz (an aluminum fluorosilicate) defines hardness 8 on the Mohs scale. Look for glassy prismatic crystals with lengthwise striations and a single perfect basal cleavage — the cleavage and superior hardness separate it from quartz, which it otherwise resembles in pegmatites and gravels.

Common lookalikes

Quartz and citrine (softer, no cleavage), aquamarine (hexagonal cross-section), fluorite (much softer, octahedral cleavage).