gemstone
Blue Topaz
Aluminum Silicate Fluoride Hydroxide, Al2SiO4(F,OH)2
Hardness: 8.0 on Mohs scale. Color: Swiss Blue. Luster: Vitreous. Crystal system: Orthorhombic. Cleavage: Perfect basal. Specific gravity: 3.49-3.57.
- Hardness
- 8
- Color
- Swiss Blue
- Luster
- Vitreous
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Physical properties
Hardness: 8.0 on Mohs scale. Color: Swiss Blue. Luster: Vitreous. Crystal system: Orthorhombic. Cleavage: Perfect basal. Specific gravity: 3.49-3.57.
Formation & geological history
Formed in igneous rocks like pegmatites and granites, as well as in alluvial deposits. While natural blue topaz exists, deep hues are typically achieved through irradiation and heat treatment of colorless topaz.
Uses & applications
Primarily used in high-quality jewelry (rings, pendants, earrings) and as a collector's gemstone. Industrial applications are limited due to high value.
Geological facts
Topaz is a pleochroic gem, meaning it can show different colors in different crystal directions. Blue topaz is the official state gemstone of Texas and the birthstone for December.
Field identification & locations
Identified by its high hardness (scratches glass/quartz) and distinct weight. In the field, look for well-defined prismatic crystals in pegmatitic veins. Commonly sourced from Brazil, Sri Lanka, and Nigeria.
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