sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: tan, yellow-brown, with dark grey patches; Luster: waxy to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 6
- Color
- tan, yellow-brown, with dark grey patches
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: tan, yellow-brown, with dark grey patches; Luster: waxy to dull; Crystal structure: trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed primarily through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids in limestone or marl beds. It can date from the Precambrian to the present.
Uses & applications
Historically used for stone tools and weapons due to its sharp edges when fractured. Modern uses include decorative gravel, lapidary work (polishing), and as a component in road construction.
Geological facts
Because it fractures conchoidally like glass, it was the primary material for arrowheads and spear points for thousands of years. It is incredibly durable and resistant to chemical weathering.
Field identification & locations
Identify in the field by its smooth, waxy texture and curved shell-like (conchoidal) fractures. It will easily scratch glass and steel. Commonly found in riverbeds or as nodules within limestone outcrops.
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