sedimentary
Agate
Silicon Dioxide (Chalcedony), SiO2
Hardness: 6.5 - 7 on the Mohs scale; Color: Variable, often white, gray, yellow, brown, or blue in concentric bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline quartz)
- Hardness
- 6
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5 - 7 on the Mohs scale; Color: Variable, often white, gray, yellow, brown, or blue in concentric bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline quartz)
Formation & geological history
Formed by the deposition of silica from groundwater in the cavities of igneous or sedimentary rocks, typically over millions of years.
Uses & applications
Used in jewelry, decorative ornaments, mortars and pestles for laboratory use, and highly prized by mineral collectors.
Geological facts
Agates often form inside volcanic vesicles (gas cavities) where silica-rich fluids deposit microscopic quartz crystals in distinct concentric layers or bands.
Field identification & locations
Identified by its distinctive banded patterns, waxy luster, and hardness that easily scratches glass. Found worldwide, notably in Brazil, Uruguay, India, and the United States.
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