sedimentary
Ironstone pebble
Ironstone (Ferruginous Sedimentary Rock)
Hardness: 4.0 - 6.0 on Mohs scale; Color: Brownish-tan to dark reddish-brown with dark oxidation patches; Luster: Earthy to sub-metallic; Texture: Fine-grained, weathered, sub-angular to rounded shape.
- Hardness
- 4
- Luster
- Earthy to sub-metallic
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Physical properties
Hardness: 4.0 - 6.0 on Mohs scale; Color: Brownish-tan to dark reddish-brown with dark oxidation patches; Luster: Earthy to sub-metallic; Texture: Fine-grained, weathered, sub-angular to rounded shape.
Formation & geological history
Formed by the accumulation and precipitation of iron-rich minerals (such as hematite, goethite, or limonite) within sedimentary layers, typically in alluvial, lacustrine, or shallow marine environments.
Uses & applications
Historically used as a low-grade iron ore; commonly collected as minor pebbles or stream gravels with little commercial utility today.
Geological facts
Ironstone nodules and pebbles often display dark manganese or iron oxide coatings (desert varnish or patina) resulting from prolonged weathering exposed to air and water.
Field identification & locations
Identified by its relatively high density compared to normal sandstone, streak test showing reddish to yellowish-brown marks, and dark oxide crusts. Widely found in riverbeds, glacial till, and sedimentary deposits globally.
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