sedimentary
Chert
Chert (Microcrystalline Quartz, SiO2)
Hardness: 7 Mohs scale; Color: typically tan, brown, or gray; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65
- Hardness
- 7 Mohs scale
- Color
- typically tan, brown, or gray
- Luster
- waxy to dull
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Physical properties
Hardness: 7 Mohs scale; Color: typically tan, brown, or gray; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, exhibits conchoidal fracture; Specific gravity: approx. 2.65
Formation & geological history
Formed primarily by the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or by chemical precipitation from silica-rich groundwater within limestone or chalk beds.
Uses & applications
Historically used for making stone tools and arrowheads because of its sharp conchoidal fracture. Modern uses include road surfacing and as a component in glass manufacturing.
Geological facts
Chert is so hard it can scratch steel. When struck against steel, it can produce sparks, leading to its historical use as flint in firearms and fire-starting kits.
Field identification & locations
Identify in the field by its smooth, shell-like fracture surfaces and its ability to scratch glass. It is often found as nodules within limestone or as bedded deposits in riverbeds.
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