mineral
Agate
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 6.5–7 on the Mohs scale. Color: Highly variable (white, grey, blue, orange, red, brown) often in concentric bands. Luster: Waxy to vitreous. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.
- Hardness
- 6
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5–7 on the Mohs scale. Color: Highly variable (white, grey, blue, orange, red, brown) often in concentric bands. Luster: Waxy to vitreous. Crystal Structure: Hexagonal (cryptocrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58–2.64.
Formation & geological history
Formed as secondary deposits in volcanic rock cavities (vugs) or ancient lavas through the rhythmic precipitation of silica from groundwater. Most specimens range from a few million to over a billion years old depending on the host rock formation.
Uses & applications
Used extensively in jewelry (cabochons, beads), decorative lapidary arts, and ornamental carvings. Historically used for making precision bearings, mortar and pestles, and seal stones.
Geological facts
Famous varieties include Lake Superior Agate, Botswana Agate, and Fire Agate. It was named by the Greek philosopher Theophrastus after the Achates River in Sicily where he first discovered it around the 4th century B.C.
Field identification & locations
Identify in the field by its distinctive waxy texture and characteristic color banding when broken. It is often found as nodules inside volcanic host rocks or as loose river stones. Common locations include Brazil, Uruguay, Germany, and the United States (specifically Lake Superior and the Pacific Northwest).
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Other mineral specimens
Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Tumbled granite
Granite, a coarse-grained felsic intrusive igneous rock
igneous
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Granite
Granite (Phaneritic intrusive igneous rock)
igneous