sedimentary
Chert (or Chalcedony)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Tan, beige, or off-white with a waxy to dull luster. Structure: Microcrystalline with conchoidal fracture. Opaque to translucent.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or off-white with a waxy to dull luster
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, beige, or off-white with a waxy to dull luster. Structure: Microcrystalline with conchoidal fracture. Opaque to translucent.
Formation & geological history
Formed primarily by the chemical precipitation of silica-rich fluids in sedimentary environments. Often occurs as nodules or layers within limestone or chalk formations. Many specimens date from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads, scrapers) due to its sharp conchoidal edges; currently used for road aggregate and as an ornamental stone in landscaping.
Geological facts
Chert is essentially the same material as flint, though 'flint' is usually used for darker varieties found in chalk. It is one of the most durable rocks, often surviving long-term weathering that dissolves surrounding limestone.
Field identification & locations
Identify in the field by its hardness (will scratch glass), waxy texture, and shell-like (conchoidal) breaking pattern. Found worldwide in riverbeds and limestone outcrops.
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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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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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