sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and grayish-mottled. Luster: Waxy to dull. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
- Hardness
- 6
- Color
- Brown, tan, and grayish-mottled
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Brown, tan, and grayish-mottled. Luster: Waxy to dull. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or by the chemical replacement of limestone/dolomite by silica-rich fluids. This specimen appears water-worn, likely from a fluvial or glacial deposit.
Uses & applications
Historically used for stone tools (flintknapping) due to its sharp edges when broken. Today used as an ornamental stone, for tumbling, and in some industrial abrasives.
Geological facts
Chert was one of the first materials used by early humans to create fire-starting tools and weaponry. Its extreme durability allows it to survive long-distance transport in rivers and glacial till.
Field identification & locations
Identify in the field by its waxy luster and smooth, curved (conchoidal) fractures if chipped. It will scratch steel and glass. Frequently found in riverbeds, gravel pits, and coastal areas.
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