sedimentary

Chert (often called Flint)

Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Tan, brownish, or gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Hardness: 6
Color: Tan, brownish, or gray
Luster: Waxy to dull

Identified March 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Tan, brownish, or gray; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. Most common in bedrock dating from the Paleozoic to Mesozoic eras.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp edges. Modernly used in road construction as aggregate, landscaping, and flint-striking fire starters.

Geological facts

Chert was one of the most important minerals for early humans. Its conchoidal fracture allows it to break into edges that are sharper than a surgical steel scalpel.

Field identification & locations

Identify in the field by its smooth, shell-like fracture pattern and ability to scratch glass. Found commonly in limestone or chalk deposits globally, particularly in the UK, USA, and France.