sedimentary

Chert (specifically Red Chert/Jasper variety)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Reddish-brown with tan/grey layers; Luster: Waxy to dull; Crystal structure: Microcrystalline (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.6 – 2.7.

Hardness: 7 on Mohs scale
Color: Reddish-brown with tan/grey layers
Luster: Waxy to dull

Identified March 23, 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 through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical precipitation of silica in groundwater. This specimen displays distinct bedding or banding common in oceanic sedimentary deposits.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used in landscaping, as a source for silica in industrial processes, and occasionally as semi-precious gemstones or decorative accents.

Geological facts

Red chert is often associated with the 'Franciscan Complex' in California. It is so hard that it can scratch steel and was used by ancient humans to create sparks for fire when struck against iron pyrites.

Field identification & locations

Identify in the field by its characteristic smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Commonly found in riverbeds, coastal cliffs, and mountain ranges with exposed sedimentary strata.

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