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 More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
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
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.
More like this
Other sedimentary specimens
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