sedimentary

Chert (Flint) with Quartz Inclusions

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Grayish-blue to brown with translucent white inclusions; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture).

Hardness: 7 on Mohs scale
Color: Grayish-blue to brown with translucent white inclusions
Luster: Waxy to vitreous

Identified July 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments where silica-rich fluids replace organic matter or precipitate out of solution within limestone or chalk beds. Often Cretaceous to Jurassic in age.

Uses & applications

Historically used for stone tools and fire-starting. Currently used in industrial abrasives, road surfacing, and as a decorative collector specimen.

Geological facts

Chert is so hard it will scratch steel. The blue-gray variety is often specifically called flint. When struck with steel, it produces sparks due to the high silica content, a property utilized by ancient humans.

Field identification & locations

Identify by its distinct conchoidal (shell-like) fracture and sharp edges when broken. Commonly found in riverbeds or within limestone outcrops. Value is generally low for raw specimens unless they have unique colors or crystal pockets.

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Clastic Sedimentary Rock Grain (SiO2 dominated)

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