sedimentary
Chert (Jasper focus)
Silicon dioxide (SiO2) - Microcrystalline Quartz
Hardness: 6.5-7 Mohs; Color: Tan, brownish-red, yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan, brownish-red, yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brownish-red, yellow; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary basins. These specimens specifically show iron oxidation common in surface weathering.
Uses & applications
Historically used for stone tools (knapping) due to sharp edges; currently used for decorative stones, landscaping, and lapidary work.
Geological facts
Chert was one of the first materials used by early humans to create fire-starting tools and weaponry. When struck against steel, it can produce sparks due to its hardness.
Field identification & locations
Identify in the field by its distinct shell-like (conchoidal) fracture pattern and its ability to scratch glass. It often feels smooth or waxy compared to surrounding limestone.
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