sedimentary

Limonite-stained Chert/Jasper

Microcrystalline Quartz (SiO2) with Iron Oxides (FeO(OH)·nH2O)

Hardness: 6.5-7 on Mohs scale. Color: Rusty brown, orange, and ochre with hints of green or tan. Luster: Dull to waxy. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: Rusty brown, orange, and ochre with hints of green or tan
Luster: Dull to waxy

Identified May 18, 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 via the accumulation of silica-rich microfossils (like radiolaria) or chemical precipitation in marine environments. The rusty coloring is due to secondary weathering and the infiltration of iron-rich groundwater (limonitization) over millions of years.

Uses & applications

Used historically for tool making (flint knapping). Today, it is used for landscaping, as a lapidary material for cabochons if the core is solid, and as a common collectible for rockhounds.

Geological facts

This specimen displays a heavy weathering rind. Iron oxides like limonite are actually a mixture of hydrous iron oxides and are a common cause of the 'rusty' appearance in sedimentary rocks.

Field identification & locations

Identified in the field by its hardness (it will scratch glass), its heavy weight relative to its size, and the characteristic orange-brown oxidation. Found globally in riverbeds, glacial tills, and sedimentary basins.

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