sedimentary
Chert (containing Iron Oxide spots)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: tan, grey, and yellow-brown; Luster: vitreous to waxy; Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 6
- Color
- tan, grey, and yellow-brown
- Luster
- vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: tan, grey, and yellow-brown; Luster: vitreous to waxy; Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. This specimen shows oxidation (yellow spots), likely from limonite or goethite.
Uses & applications
Historically used for stone tools (arrowheads, scrapers); currently used in road construction, as decorative stone, or for starting fires (flint equivalent).
Geological facts
Chert is so hard it can scratch glass and sparks when struck against steel. It was one of the most vital resources for prehistoric humans due to its sharp edges when fractured.
Field identification & locations
Identify in the field by its smooth, waxy feel and circular 'conchoidal' fractures. It is commonly found in limestone or chalk beds and along riverbanks.
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