gemstone
Blue Topaz (Cut Gemstone)
Aluminum silicate fluoride hydroxide (Al2SiO4(F,OH)2)
Hardness: 8, Color: Swiss/Sky Blue (treated), Luster: Vitreous, Crystal structure: Orthorhombic, Specific Gravity: 3.4–3.6
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Physical properties
Hardness: 8, Color: Swiss/Sky Blue (treated), Luster: Vitreous, Crystal structure: Orthorhombic, Specific Gravity: 3.4–3.6
Formation & geological history
Formed in igneous rocks like granite and rhyolite through pneumatolytic processes involving fluorine-rich vapors. Natural blue is rare; most faceted blue topaz is irradiated and heated clear topaz.
Uses & applications
Predominantly used in commercial jewelry as a affordable alternative to aquamarine or sapphire.
Geological facts
Topaz is pleochroic, meaning it can show different colors in different crystal directions. It holds the title of the state gemstone of Texas and Utah (different varieties).
Field identification & locations
Identify in the field by its high hardness (scratches glass/quartz) and heavy feel (high specific gravity). Often found in alluvial deposits or pegmatite veins.
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