sedimentary

Chert (Greenish-Grey variety)

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Dull greenish-grey with slight translucency; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Dull greenish-grey with slight translucency
Luster: Waxy to vitreous

Identified June 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from seawater or the accumulation of siliceous biological remains (like diatoms or radiolarians). It often occurs as nodules or layers in limestone or shale and can range from Precambrian to modern ages.

Uses & applications

Historically used for stone tools and starting fires (flint); currently used as abrasive media, road surfacing aggregate, and occasionally for lapidary work in jewelry.

Geological facts

Chert was a primary technology for early humans due to its conchoidal fracture which produces razor-sharp edges. It is chemically identical to quartz but contains impurities that give it various colors.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy appearance, and sharp, curved fracture patterns. Common in marine sedimentary basins and riverbeds as smoothed pebbles.