sedimentary

Chert (Iron-stained)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Dark brown to black with iron-oxide staining; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Dark brown to black with iron-oxide staining
Luster: Waxy to dull

Identified March 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (diatoms, radiolarians) or chemical precipitation from groundwater within sedimentary layers. This specific piece shows significant weather-induced iron oxidation.

Uses & applications

Historically used for stone tools and starting fires (flint); currently used in road construction, as an abrasive, and by lapidary hobbyists for tumbling or jewelry.

Geological facts

Because of its high silica content and density, chert was a primary material for prehistoric arrowheads and scrapers. It can range in color from white to pitch black depending on impurities.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and steel) and its shell-like conchoidal fracture patterns. Found globally in limestone beds or as stream gravel.

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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