ironstone

Ironstone is a hard, iron-rich sedimentary rock that is noncherty and has a clastic texture. Unlike banded iron formations (BIFs), which are regionally extensive, ironstones are typically found in local areas.123

Ironstones are primarily from the Phanerozoic Eon, with most dating to the Early Paleozoic and Jurassic periods, though some can be much older. They are usually found in basins no larger than 150 kilometers across and contain iron minerals like goethite, hematite, and chamosite.1

The origin of ironstones is not fully understood, but they are thought to form from the erosion and redeposition of iron-rich soils. They often exhibit oolitic textures and features like cross-bedding and ripple marks, suggesting deposition in shallow marine environments.1