sedimentary

Chert (Green River Chert)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Olive green to dull tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Olive green to dull tan
Luster: Waxy to vitreous

Identified June 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Olive green to dull tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the precipitation of silica from groundwater or the accumulation of silica-rich organic debris (like radiolarians) in marine or lake environments. This specimen appears to be a water-worn river pebble.

Uses & applications

Historically used for stone tools (flintknapping) due to its sharp edges; used today as decorative gravel, in landscaping, and as a low-cost lapidary material.

Geological facts

The red spots visible on this rock are likely Clover Mites (Bryobia praetiosa) or Velvet Mites, rather than part of the mineralogy. Chert is so hard it can scratch steel and was used to start fires before matches.

Field identification & locations

Identify in the field by its waxy texture, curved (conchoidal) fractures similar to glass, and its ability to scratch glass or steel. Found globally in limestone beds or as river cobbles.