sedimentary

Chert (specifically Jasper/Agate variety)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Brown, red, and blue-grey bands. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.65.

Hardness: 6
Color: Brown, red, and blue-grey bands
Luster: Waxy to vitreous

Identified June 21, 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 primarily from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or through chemical precipitation in marine or volcanic environments. This specimen likely formed as a nodule in sedimentary limestone or within volcanic cavities.

Uses & applications

Historically used for stone tools (knapping) due to its sharp conchoidal fracture. Currently used for lapidary work, jewelry, and as a collector's specimen.

Geological facts

Chert is one of the most durable rocks and has been used by humans for millions of years to create tools. The variety known as 'flint' is often dark, while 'jasper' is generally opaque and red or brown.

Field identification & locations

Identifiable in the field by its hardness (will scratch glass), conchoidal fracture (smooth, curved breaks), and waxy appearance. Often found in riverbeds or eroded out of limestone cliffs.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Cone-in-cone structure (Limestone)

Cone-in-cone structure (Secondary Sedimentary Structure)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary