sedimentary

Chert (specifically White Chert or Novaculite)

Silicon Dioxide (SiO₂)

Hardness: 7 (Mohs scale); Color: White, ivory, with tan/orange iron staining; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 7 (Mohs scale)
Color: White, ivory, with tan/orange iron staining
Luster: Dull to waxy

Identified March 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the chemical replacement of limestone/chalk by silica-rich fluids. Generally found in Paleozoic or Mesozoic age strata.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used for road base, decorative landscaping, and as an abrasive in stone-washed denim production.

Geological facts

Chert is so hard it will spark when struck against steel. Indigenous peoples prized high-quality white chert for its predictability when 'knapping' or shaping into tools.

Field identification & locations

Identify by its extreme hardness (will scratch glass) and smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds or as nodules within limestone outcrops. Collectors look for pieces with 'translucency' at the edges.

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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