sedimentary

Chert (specifically Flint or Common Opal fragment)

Cryptocrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs scale), Color: tan, white, and waxy brown, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline (microscopic quartz), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6

Hardness: 6

Identified June 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of organisms or precipitation from silica-rich groundwater within limestone or chalk beds. Often associated with Cretaceous or older marine deposits.

Uses & applications

Historical use for stone tools (knapping) due to sharp edges; currently used for road surfacing, jewelry (if colorful), and as fire-starting flint.

Geological facts

Chert and flint were among the first materials used by prehistoric humans to create spearheads and knives because of their predictable conchoidal fracture which creates razor-sharp edges.

Field identification & locations

Identify by its waxy texture and shell-like (conchoidal) breakage patterns. It will easily scratch glass. Commonly found as nodules in limestone outcrops or as river-worn pebbles.