Topacio

Topaz is an aluminium- and fluorine-bearing nesosilicate with Mohs hardness 8, perfect cleavage and vitreous lustre; hard to scratch yet brittle on fracture due to its cleavage.

In volcanic cavities it is much less common than in pegmatitic settings. In such voids it may show free vertical growth, internal zoning and well-developed faces. Crystals can display more irregular forms and interrupted growth, recording the eruptive environment. In rhyolites it is uncommon, where space usually limits development.

The imperial variety is distinguished by a warm colour range, high transparency and a prismatic habit. It is recognised by golden, honey and orange hues. Brazilian pieces are regarded as the world standard for quality and typicity.

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