mineral
Chalcedony (Botryoidal)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 (Mohs); Color: Translucent white to milky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64
- Hardness
- 6
- Color
- Translucent white to milky grey
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Translucent white to milky grey; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58-2.64
Formation & geological history
Formed through the deposition of silica from low-temperature hydrothermal fluids or groundwater in cavities of igneous or sedimentary rocks. This specimen shows a 'botryoidal' or grape-like habit commonly associated with volcanic vugs.
Uses & applications
Used primarily for lapidary work (cabs and beads), ornamental stone carvings, and as a collectible geological specimen. High-purity silica is used in optics and electronics.
Geological facts
Chalcedony is actually composed of two different minerals: quartz and moganite. The name is derived from the ancient Greek town of Chalcedon in Asia Minor. It was highly valued in antiquity for cylinder seals and amulets because it does not stick to hot wax.
Field identification & locations
Identify in the field by its waxy luster, conchoidal fracture, and rounded 'bubbly' surface texture. It is harder than steel and will scratch glass. Commonly found in desert regions of the SW United States, Brazil, and Iceland.
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