sedimentary
Chert (Iron-Stained)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7.0 (Mohs scale); Color: tan, yellow, orange, or brown from iron oxides; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 6
- Color
- tan, yellow, orange, or brown from iron oxides
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7.0 (Mohs scale); Color: tan, yellow, orange, or brown from iron oxides; Luster: waxy to dull; Structure: microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed from the recrystallization of silica in sedimentary environments, often through the accumulation of siliceous skeletal remains (diatoms/radiolarians) or precipitation from groundwater. Age varies from Precambrian to modern.
Uses & applications
Historically used for making stone tools (arrowheads/scrapers) due to its sharp edges; and currently used as road aggregate, in landscaping, and as a collector's specimen.
Geological facts
Chert possesses a conchoidal fracture, allowing it to break into razor-sharp edges. It is chemically identical to quartz but with a much finer crystal structure that makes it look opaque or waxy.
Field identification & locations
Identify in the field by its smooth, waxy feel and shell-like (conchoidal) breaking patterns. It will easily scratch glass. Commonly found in limestone or dolomite beds as nodules or layers.
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