sedimentary
Chert (Jasper/Chalcedony)
Silicon dioxide (SiO2) - Microcrystalline quartz
Hardness: 6.5-7 Mohs scale; Color: Tan, brown, and cream; Luster: Waxy to dull; Breakdown: Conchoidal fracture; Transparency: Opaque to translucent
- Hardness
- 6
- Color
- Tan, brown, and cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 6.5-7 Mohs scale; Color: Tan, brown, and cream; Luster: Waxy to dull; Breakdown: Conchoidal fracture; Transparency: Opaque to translucent
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. Can be found in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools (knapping) due to its sharp edges; currently used for lapidary work, jewelry, and as a collector's specimen.
Geological facts
Chert is one of the most common materials used by prehistoric humans for arrowheads and spear tips because it fractures like glass to create razor-sharp edges.
Field identification & locations
Identify by its waxy appearance, extreme hardness (it will scratch glass), and its smooth, curved conchoidal fractures. Commonly found in riverbeds or limestone outcrops.
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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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Clastic Sedimentary Rock Grain (SiO2 dominated)
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