sedimentary
Chert (Yellow or Brown Jasper)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, brown, ochre; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 6
- Color
- Tan, brown, ochre
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, brown, ochre; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite. It is found in deposits ranging from Precambrian to Cenozoic eras.
Uses & applications
Historically used for stone tools (flintknapping). Modernly used in geological collections, landscaping, and occasionally as a low-cost gemstone for cabochons.
Geological facts
Jasper is a variety of chert that gets its opaque color from high concentrations of iron oxides. It is so tough that it was one of the primary materials used by prehistoric humans to make arrowheads and scrapers.
Field identification & locations
Identify in the field by its waxy texture, smooth rounded edges (if river-worn), and conchoidal (shell-like) fracture patterns if chipped. It will easily scratch glass and steel.
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Cone-in-cone structure (Limestone)
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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