Topaz crystallises in the orthorhombic system. It is usually colourless, but can occur in a number of colours - blue, orange, brown, green or pink.
Properties of topaz
- Chemistry: Aluminium fluorine silicate
- Hardness: 8
- Refractive Index: 1.610 - 1.638
- Specific gravity: 3.53 - 3.56
- Lustre: vitreous
Topaz crystals, usually colourless to pale blue, are found at a number of sites in Australia, with the finest gem material coming from Oban in New South Wales, Mt Surprise in Queensland and Flinders Island in Tasmania.
New South Wales
In New South Wales, the Oban and Mitchell Rivers in the New England area have yielded quantities of fine topaz. It occurs as waterworn crystals, cleavage fragments and pebbles. Many large, clear gemstones have been faceted from this material.