sedimentary

Ironstone (likely siderite or goethite-rich siltstone)

Ferruginous Siltstone

AI-generated identification · may be incorrect

Hardness: 3.5-5.5 (Mohs); Color: Dark brown to reddish-brown; Luster: Dull to earthy/sub-metallic; Structure: Fine-grained, often massive or layered; Specific Gravity: 3.0-3.9

Hardness: 3
Color: Dark brown to reddish-brown
Luster: Dull to earthy/sub-metallic

Identified April 10, 2026More sedimentary →

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Physical properties

Hardness: 3.5-5.5 (Mohs); Color: Dark brown to reddish-brown; Luster: Dull to earthy/sub-metallic; Structure: Fine-grained, often massive or layered; Specific Gravity: 3.0-3.9

Formation & geological history

Formed through the chemical precipitation of iron-rich minerals in aqueous environments, often during the Paleozoic or Mesozoic eras. It frequently occurs in marine or swampy environments where iron oxides accumulate between sedimentary layers.

Uses & applications

Historically used as a low-grade iron ore; occasionally used as a durable construction stone or landscape rock in garden design.

Geological facts

Ironstone 'nodules' or 'concretions' can sometimes contain perfectly preserved fossils in the center, such as leaves or fish, particularly in famous locations like the Mazon Creek formation.

Field identification & locations

Identify by its high density compared to other sedimentary rocks and its characteristic rusty-brown streak. Check if it is slightly magnetic, which can indicate magnetite content within the ironstone.