sedimentary
Chert (Nodule)
Chert (Silicon dioxide, SiO2)
Hardness: 6.5-7 Mohs; Color: Tan, white, and creamy grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Tan, white, and creamy grey
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 Mohs; Color: Tan, white, and creamy grey; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed via the accumulation of siliceous remains of microscopic organisms or by chemical precipitation from silica-rich groundwater within limestone or chalk beds. Often found in Phanerozoic sedimentary layers.
Uses & applications
Historically used for stone tools (arrowheads). Modernly used as an abrasive, in road construction, and as decorative gravel.
Geological facts
Chert is essentially the same mineral as flint, though the term 'flint' is often reserved for dark gray or black nodules found in chalk. It is highly resistant to weathering and often survives as a stream pebble.
Field identification & locations
Identify by its non-porous, waxy appearance and conchoidal (shell-like) fracture edges. Commonly found in riverbeds and limestone outcrops.
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