sedimentary

Oolitic Ironstone

Sedimentary Ooidal Ironstone (Limonite/Hematite mixture)

AI-generated identification · may be incorrect

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 →

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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.