sedimentary

Chert (specifically Banded Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically gray, tan, or brown with distinct lighter/darker bands; Luster: waxy to dull; Structure: microcrystalline (no visible crystals); Cleavage: none (fractures conchoidally); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Luster: waxy to dull

Identified March 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids within limestone or chalk beds. Often Paleozoic or Mesozoic in age.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in construction aggregate, road surfacing, and as a polishing media in rock tumblers.

Geological facts

Because it breaks with a conchoidal fracture like glass, it was one of the most important minerals for prehistoric survival. It is so chemically stable that it often remains intact long after the surrounding limestone has weathered away.

Field identification & locations

Identify in the field by its hardness (it will scratch glass or steel) and its smooth, shell-like fracture surfaces. It often feels 'slicker' than surrounding limestone. Commonly found in riverbeds or eroding out of limestone cliffs.