mineral
Chalcedony (Agate / Quartz Pebble)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs, Color: Milky white, pale grey, translucent, Luster: Waxy to vitreous, Crystal structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.64.
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 Mohs, Color: Milky white, pale grey, translucent, Luster: Waxy to vitreous, Crystal structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.64.
Formation & geological history
Formed through the deposition of silica-rich solutions at low temperatures in cavities, fractures, and sedimentary beds, often smoothed by water erosion.
Uses & applications
Used in lapidary art, tumble polishing, jewelry (beads, cabochons), carving, and general rock collecting.
Geological facts
Cryptocrystalline quartz varieties like chalcedony are composed of extremely fine intergrowths of quartz and moganite, giving them a smooth, waxy surface when rounded or polished.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy feel, translucency around edges, and smooth water-worn surface along riverbeds, beaches, or gravel deposits.
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