sedimentary

Chert (and Flint variant)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 on Mohs scale
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 29, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Microcrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich biogenic material such as radiolarian or diatoms, or by chemical precipitation in groundwater replacing limestone/chalk. Found throughout Earth's history from Precambrian to modern times.

Uses & applications

Historically used for stone tools and starting fires (flint). Currently used in road surfacing, as an abrasive, and for decorative landscaping.

Geological facts

Chert was one of the first materials harvested by early humans to create arrowheads and scrapers due to its sharp edges when broken. 'Flint' is a dark variety of chert commonly found in chalk deposits.

Field identification & locations

Identify by its waxy appearance and shell-like (conchoidal) curves on broken faces. It will scratch glass easily. Commonly found as nodules or layers in limestone beds.