sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, ochre; Luster: Dull to waxy; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 6
- Color
- Tan, brown, ochre
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, ochre; Luster: Dull to waxy; Structure: Cryptocrystalline/microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica from groundwater filling voids in limestone or chalk, or from the accumulation of siliceous remains such as radiolaria or diatoms. These can date back to the Precambrian era.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its conchoidal fracture. Modern uses include landscaping, construction aggregate, and as semiprecious stones in jewelry (as Jasper).
Geological facts
This specimen shows significant pitting and weathering, indicating it may have been tumbled in a river or exposed to erosive elements for a long period. Chert is so hard it can create sparks when struck against steel.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its smooth waxy fracture surface, and its lack of visible grains. Commonly found in sedimentary basins and riverbeds.
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