sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, grey, or black with a weathered exterior; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, grey, or black with a weathered exterior
Luster: Waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater or the accumulation of silica-rich microfossils in limestone or chalk beds. Commonly found in sedimentary basins worldwide.

Uses & applications

Historically used for stone tools (flintknapping); currently used as an abrasive, decorative stone in landscaping, or for gravel construction.

Geological facts

Chert is one of the most durable sedimentary rocks and was the primary material for prehistoric arrowheads and spear points due to its sharp edges when broken.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel nail) and characteristic conchoidal fracture patterns similar to thick glass. Look for rounded or irregular lumps in limestone outcrops.