sedimentary
Chert (Jasper variation)
Silicon dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown to tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Microcrystalline quartz); Cleavage: None (Conchoidal fracture); Specific gravity: 2.58-2.91
- Hardness
- 6
- Color
- Reddish-brown to tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown to tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline (Microcrystalline quartz); Cleavage: None (Conchoidal fracture); Specific gravity: 2.58-2.91
Formation & geological history
Formed by the accumulation of siliceous remains of organisms or chemical precipitation from silica-rich fluids. Common in sedimentary sequences such as limestone or shale beds across many geological eras.
Uses & applications
Historical use for stone tools/weapons; modern use in landscaping, aggregate, and occasionally semi-precious jewelry or lapidary art.
Geological facts
Chert was one of the most important minerals for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and scrapers.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy luster, and shell-like (conchoidal) fracture surfaces. Commonly found in nodules or beds within sedimentary rock layers.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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