sedimentary
Agate
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 (Mohs), Color: Translucent grey/brown/white with banding, Luster: Waxy to vitreous, Crystal Structure: Trigonal (cryptocrystalline), Cleavage: None, Specific Gravity: 2.58–2.64
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs), Color: Translucent grey/brown/white with banding, Luster: Waxy to vitreous, Crystal Structure: Trigonal (cryptocrystalline), Cleavage: None, Specific Gravity: 2.58–2.64
Formation & geological history
Forms primarily in volcanic and metamorphic rocks as a deposit from silica-rich groundwater filling cavities (vugs) in host rock.
Uses & applications
Used widely in lapidary arts for jewelry, ornaments, and polished stones; also used for heavy-duty mortars and pestles because of its hardness.
Geological facts
Agate is named after the Achates River in Sicily where it was first discovered; it has a long history of use as an amulet to protect against negative energy.
Field identification & locations
Identify in the field by its translucency when held to light and its smooth, waxy texture. Commonly found in riverbeds and volcanic regions like Brazil, Mexico, and Lake Superior.
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