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Rock guide

Chert / Flint

rock · common

Quick facts

Formula
SiO2
Hardness
6.5–7
Luster
Waxy to dull
Colors
Gray, tan, black, brown

Microcrystalline quartz rock. Conchoidal fracture. Flint is a dark variety historically used for tools.

Color alone cannot separate chert, jasper, and some agates. Fracture and translucency matter.

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