sedimentary

Chert (specifically Banded Chert)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

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 →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

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.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary