Topaz is a mineral with chemical formula Al2SiO4 (F, OH)2. It has vitreous luster, and occurs in various colours including yellow, orange, blue, pink, green and colourless, while the streak is white. Topaz has orthorhombic crystal system and usually forms columnar crystals, and its hardness is 8. Topaz is usually produced in pegmatite, geode and hydrothermal W-Sn quartz vein during late stage magma differentiation of granite. Small amount of topaz can be found in quartz veins at San Shek Wan, Hong Kong. Topaz is suitable for producing jewellery because of its high hardness, clear transparency and rich of colours. The colour of topaz changes to blue after irradiation treatment.
Our Society - GSHK
The Geological Society of Hong Kong is a non-profit organisation that attempts to promote geological and earth science studies within Hong Kong and the adjacent region.
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