sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Opaque brown, tan, and cream bands. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- Opaque brown, tan, and cream bands
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Opaque brown, tan, and cream bands. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the accumulation of silica-rich fluids in sedimentary environments or by the replacement of calcium carbonate. Typically found in limestone or dolomite deposits.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; used in jewelry as semi-precious gemstones (jaspers); occasionally used as decorative aggregate.
Geological facts
Chert was one of the most important minerals for early humans to create arrowheads and scrapers. The variety Jasper is defined by its high iron oxide content which provides the earthy colors.
Field identification & locations
Identify in the field by its hardness (can scratch glass) and its curved, glass-like 'conchoidal' fracture patterns. Look for it in riverbeds or as nodules within limestone outcrops.
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