sedimentary

Chert (Yellow Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Yellow (due to iron oxide inclusions), tan, or mustard; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65.

Hardness: 6
Color: Yellow (due to iron oxide inclusions), tan, or mustard
Luster: Dull to waxy

Identified February 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 through the accumulation of silica-rich fluids or the replacement of limestone. It typically forms in marine environments where silica-rich organic remains (like radiolaria or diatoms) recrystallize over millions of years.

Uses & applications

Historical use in stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include lapidary work, jewelry (cabs), and as a decorative landscaping stone.

Geological facts

Yellow chert or jasper has been used by humans for over 100,000 years. Because of its extreme hardness and ability to hold a sharp edge, it was a primary material for prehistoric survival tools.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Widely found in riverbeds, glacial tills, and within limestone outcrops. Collectors look for pieces with unique patterns or deep coloration.

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