gemstone
Blue Topaz
Aluminum Silicate Fluoride Hydroxide (Al2SiO4(F,OH)2)
Hardness: 8, Color: Blue (enhanced), Luster: Vitreous, Crystal Structure: Orthorhombic, Cleavage: Perfect basal, Specific Gravity: 3.49-3.57
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Physical properties
Hardness: 8, Color: Blue (enhanced), Luster: Vitreous, Crystal Structure: Orthorhombic, Cleavage: Perfect basal, Specific Gravity: 3.49-3.57
Formation & geological history
Formed during the final stages of cooling in igneous rocks like pegmatites and rhyolitic lava flows. Most blue topaz is originally colorless and achieves its color via irradiation and heat treatment.
Uses & applications
Primarily used in high-quality jewelry (rings, pendants, earrings), and as a birthstone for December.
Geological facts
Colorless topaz is the most common variety; natural deep blue topaz, known as 'London Blue,' is extremely rare in nature. The gemstone in the photo resembles the 'Swiss Blue' shade achieved through treatment.
Field identification & locations
Identified by its high hardness (not scratched by quartz) and high specific gravity. It is the state gemstone of Texas and Utah. Found commonly in Brazil, Nigeria, and Sri Lanka.
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