sedimentary

Oolitic Ironstone

Sedimentary Ooidal Ironstone (Limonite/Hematite mixture)

Hardness: 5-6 (variable); Color: Ochre, rusty brown, or mustard yellow; Luster: Dull to sub-metallic; Crystal structure: Amorphous to microcrystalline; Cleavage: None; Notable for rounded 'ooid' grains resembling fish roe.

Hardness: 5-6 (variable)
Color: Ochre, rusty brown, or mustard yellow
Luster: Dull to sub-metallic

Identified March 15, 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 in shallow-marine environments where iron-rich waters precipitate minerals around a nucleus (like a sand grain or shell fragment) in rolling waves. Most common in Paleozoic and Mesozoic strata.

Uses & applications

Historically used as a major source of iron ore for steel manufacturing; today it is primarily a geological specimen or used for decorative architectural stones.

Geological facts

The 'ooids' forming the texture are typically less than 2mm in diameter. These rocks were the backbone of the British iron industry during the Industrial Revolution, found extensively in the Cleveland Hills.

Field identification & locations

Identify by looking for small, spherical concentrically-layered grains (ooids) that have been cemented together. Often reacts slightly with acid if the cement is calcareous. Found in iron-rich sedimentary basins worldwide.

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