sedimentary

Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Brownish-yellow to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brownish-yellow to tan
Luster: Waxy to dull

Identified May 17, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brownish-yellow to tan; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of siliceous oozes on the ocean floor or through the replacement of limestone. It is a chemical or biochemical sedimentary rock common in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for making stone tools due to its sharp edges; currently used as a road aggregate, in landscaping, and as a semi-precious gemstone.

Geological facts

Chert is so hard it can scratch steel. When struck against steel, it produces sparks, which led to its use in flintlock firearms.

Field identification & locations

Identify by its smooth, waxy feel and circular (conchoidal) shell-like fracture patterns. Commonly found in riverbeds or as nodules within limestone outcrops.