sedimentary

Chert (and Limestone)

Silicon Dioxide (SiO2) in Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 7 (chert) to 3 (limestone); Color: buff, tan, white, and earthy yellow; Luster: dull to waxy; Texture: fine-grained/cryptocrystalline; Fractures: conchoidal (shell-like) in the chert portions.

Hardness: 7 (chert) to 3 (limestone)
Color: buff, tan, white, and earthy yellow
Luster: dull to waxy

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within marine limestone beds. Common in sedimentary basins worldwide, particularly in Paleozoic and Mesozoic strata.

Uses & applications

Historically used for stone tools/arrowheads. Today used primarily as road base, construction aggregate, and occasionally as a decorative landscape stone.

Geological facts

Chert is so hard it can spark when struck against steel. It is chemically identical to quartz but has a different micro-crystalline structure. This specific specimen appears to be a weathered fragment with some iron-oxide staining.

Field identification & locations

Identify by its hardness (chert will scratch glass) and its association with softer limestone that often fizzes in weak acid. Generally found in gravel pits, riverbeds, or limestone outcrops.