sedimentary

Chert (Smooth River Siltstone/Basalt variant)

Silicon dioxide (SiO2) / Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs. Color: Dull grey, greenish-grey, or black. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Hardness: 6
Color: Dull grey, greenish-grey, or black
Luster: Dull to waxy

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs. Color: Dull grey, greenish-grey, or black. Luster: Dull to waxy. Structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.

Formation & geological history

Formed through the precipitation of silica from seawater or the accumulation of silica-rich organic debris (such as radiolarians or diatoms) on the ocean floor. Most specimens are from the Paleozoic or Mesozoic era.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when broken. Also used in construction aggregate, road base, and as a durable river stone in landscaping.

Geological facts

Chert is so hard it can scratch glass and steel. It was one of the most important commodities for prehistoric humans for crafting sharp cutting edges. When struck against steel, it can produce sparks, similar to flint.

Field identification & locations

Identify by its extreme hardness, waxy texture, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds, glacial tills, and as nodules within limestone layers.