sedimentary
Chert (var. Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: typically tan, yellow, and green/grey banding; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture.
- Hardness
- 6
- Color
- typically tan, yellow, and green/grey banding
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: typically tan, yellow, and green/grey banding; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, conchoidal fracture.
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (arrowheads). Modern uses include gemstones, tumbled stones, landscaping, and industrial abrasives.
Geological facts
Chert is so hard it can create sparks when struck against steel. The green and yellow banding in this specimen is often caused by iron and chlorite impurities within the silica matrix.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its waxy feel, and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in riverbeds and gravel pits.
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