sedimentary
Chert (varieties include Flint and Jasper)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically gray, white, orange, or brown; Luster: waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: none, conchoidal fracture
- Hardness
- 7 on Mohs scale
- Color
- typically gray, white, orange, or brown
- Luster
- waxy to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: typically gray, white, orange, or brown; Luster: waxy to vitreous; Crystal Structure: Trigonal (microscopic); Cleavage: none, conchoidal fracture
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. It often forms as nodules or bedded layers.
Uses & applications
Historically used for stone tools and weapons. Used in modern industry as grinding media and in road construction. High-quality specimens are used for jewelry (as agate or jasper) and lapidary art.
Geological facts
Chert was one of the most important raw materials for early humans because its conchoidal fracture creates extremely sharp edges; it can also be used with steel to generate sparks for fire starting.
Field identification & locations
Identify by its waxy luster, smooth conchoidal (shell-like) fractures, and its ability to scratch glass easily. Commonly found in limestone beds or as river cobbles.
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