sedimentary
Agate
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Pale blue to white. Luster: Waxy to vitreous. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, conchoidal fracture.
- Hardness
- 6
- Color
- Pale blue to white
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Pale blue to white. Luster: Waxy to vitreous. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, conchoidal fracture.
Formation & geological history
Forms when silica-rich groundwater fills cavities (vugs) in volcanic or sedimentary rocks. The silica precipitates in layers, often over millions of years, found in primary deposits or as secondary pebbles in rivers.
Uses & applications
Used extensively in jewelry (cabochons), precision weighs, mortar and pestles, and as a popular ornamental stone for collectors and lapidary artists.
Geological facts
Agate was named by the Greek philosopher Theophrastus who discovered the stone along the shore line of the river Achates in Sicily. No two agates are exactly alike in pattern or internal structure.
Field identification & locations
Identify by its characteristic banding (though sometimes subtle in small pieces), waxy texture, and translucency. Commonly found in riverbeds, lake shores, and gravel pits in volcanic regions.
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