sedimentary
Chert (Iron-rich or Jasperoid)
Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs scale; Color: Rusty brown, tan, and dark gray; Luster: Dull to waxy; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
- Hardness
- 6
- Color
- Rusty brown, tan, and dark gray
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs scale; Color: Rusty brown, tan, and dark gray; Luster: Dull to waxy; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7
Formation & geological history
Formed through the precipitation of silica from groundwater or within deep-sea sedimentary deposits. Iron impurities give it the brownish-red hue. It can be found in strata dating from the Precambrian to the present.
Uses & applications
Historically used for stone tools (flintknapping). Modern uses include construction aggregate, road base, and common decorative landscaping stone or as lapidary material for tumbling.
Geological facts
Chert is so durable it often survives long after the surrounding rock has weathered away. Ancient people used its predictable conchoidal fracture to create sharp arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its sharp, shell-like fracture patterns (conchoidal). It is common globally, often found in limestone or dolomite beds and as river cobbles.
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