Ironstone with Limonite/Goethite coating

Physical Properties

Hardness: 4-5.5 on Mohs scale; Color: Dark brown, reddish, to yellowish-brown; Luster: Dull, earthy; Crystal structure: Amorphous or microcrystalline; Density: High (feels heavy for its size)

Formation & Geological History

Formed through the precipitation of iron oxides from water or the chemical weathering of iron-rich minerals. Often found in bog environments or as a secondary alteration in sedimentary layers.

Uses & Applications

Historically used as a low-grade iron ore. Today, it is primarily used in landscaping, as a pigment (ochre), or as a road-building material in specific regions.

Geological Facts

Ironstone was a primary source of iron for the early Industrial Revolution in Europe and the United Kingdom. Its reddish-brown stain is due to the oxidation of iron, essentially geological rust.

Field Identification & Locations

Identify in the field by its significant weight (high specific gravity) and its characteristic rusty streak left when rubbed on unglazed porcelain. Commonly found in sedimentary basins and weathered outcrops.

Identified on: 4/20/2026

Mode: Standard