sedimentary
Chert (Jasper variation)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 (Mohs scale), Color: Brownish-yellow with streaks, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline (cannot see grains), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
- Hardness
- 6
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Physical properties
Hardness: 6.5-7 (Mohs scale), Color: Brownish-yellow with streaks, Luster: Waxy to dull, Crystal Structure: Microcrystalline/Cryptocrystalline (cannot see grains), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments. Often found as nodules or layers within limestone or dolostone beds.
Uses & applications
Historically used for stone tools and arrowheads. Currently used in landscaping, as aquarium decor, and polished as semi-precious gemstones for jewelry (Jasper).
Geological facts
Chert breaks with a conchoidal (shell-like) fracture, creating sharp edges that were essential for early humans to create hunting tools and scrapers.
Field identification & locations
Identify in the field by its hardness (it can scratch glass and steel) and waxy appearance. Common in riverbeds and limestone outcrops worldwide.
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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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