mineral
Chalcedony (Agate and Carnelian varieties)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: translucent orange, brown, grey, and milky white, Luster: waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Specific Gravity: 2.58-2.64
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: translucent orange, brown, grey, and milky white, Luster: waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Specific Gravity: 2.58-2.64
Formation & geological history
Formed through the deposition of silica from groundwater in cavities of igneous and sedimentary rocks. These are likely water-worn river pebbles or tumbled specimens.
Uses & applications
Used in jewelry (cabochons, beads), decorative carvings, and as therapeutic 'pocket stones'. Also used industrially for mortar and pestles due to hardness.
Geological facts
Chalcedony was used in the ancient world for making cylinder seals and signet rings because hot wax does not stick to it. Agate is a variety specifically known for its banding, though these pieces appear mostly solid or mossy.
Field identification & locations
Identify by its waxy luster, lack of visible crystals, and inability to be scratched by a steel knife. Commonly found in riverbeds, beaches, and volcanic regions worldwide.
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Arenite (SiO2 based)
sedimentary
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Metamorphic
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metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
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Nephrite
Mineral/Rock
Granite
Granite (Phaneritic intrusive igneous rock)
igneous