sedimentary

Chert (Iron-stained)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: tan, white, and reddish-brown due to hematite staining, Luster: waxy to dull, Structure: microcrystalline quartz, Cleavage: none (conchoidal fracture)

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, white, and reddish-brown due to hematite staining, Luster: waxy to dull, Structure: microcrystalline quartz, Cleavage: none (conchoidal fracture)

Formation & geological history

Formed as a chemical precipitate from silica-rich fluids or the accumulation of siliceous remains of organisms like diatoms and radiolaria. Found in sedimentary basins.

Uses & applications

Used historically for stone tools due to sharp edges; currently used for landscaping, road base, and as a decorative stone in gardening.

Geological facts

Chert is extremely durable and chemically resistant. It often occurs as nodules or beds within limestone or chalk formations. Iron-stained varieties are often colloquially called jasper if opaque and colorful.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Commonly found in river beds or landscaping mulch.