sedimentary
Chert
Microcrystalline Quartz (SiO2)
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
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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.
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