sedimentary

Chert Nodule

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Cream, tan, or light grey, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Cream, tan, or light grey, Luster: Waxy to dull, Structure: Cryptocrystalline, Fracture: Conchoidal

Formed via chemical precipitation of silica-rich fluids within limestone or chalk beds. Often Cretaceous or Paleozoic in age.

Historically used for stone tools; currently used in construction aggregate and as a collector specimen.

Chert is so hard it can scratch glass and steel. It was a primary material for making arrowheads and spear points in pre-colonial times.

Identify by its smooth, waxy feel and sharp, shell-like edges when broken. Commonly found in river beds or weathering out of limestone cliffs.

Sandstone or Siltstone

Arenite (if sandstone)

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

Shale or Slaty Mudstone

Argillaceous sedimentary rock

Sandstone

Arenite (primarily SiO2)