mineral
Chalcedony
Chalcedony (cryptocrystalline Silicon Dioxide, SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Translucent white to milky tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture
- Hardness
- 6
- Color
- Translucent white to milky tan
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Translucent white to milky tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Conchoidal fracture
Formation & geological history
Forms when silica-rich fluids deposit in cavities or fractures of volcanic or sedimentary rocks at low temperatures. Common in geode linings and as a major component of chert and agate.
Uses & applications
Used extensively in jewelry as cabochons, for carvings, and as a raw material for sandpaper and industrial abrasives due to its hardness and durability.
Geological facts
Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without significant magnification. It was highly prized in the ancient world for carving cylinder seals.
Field identification & locations
Identify in the field by its waxy luster, hardness (it will scratch glass), and lack of visible crystal faces. Found worldwide, especially in areas with basaltic volcanic history.
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