sedimentary
Ironstone Pebble
Iron-rich Sedimentary Rock (Fe2O3 / FeO(OH))
Hardness: 5.0 - 6.5 on Mohs scale. Color: reddish-brown, dark brown, or ochre. Luster: dull to earthy. Structure: fine-grained, rounded by stream or coastal erosion. Specific gravity: 3.0 - 4.3 (denser than typical silicate rocks due to iron content).
- Hardness
- 5
- Color
- reddish-brown, dark brown, or ochre
- Luster
- dull to earthy
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Physical properties
Hardness: 5.0 - 6.5 on Mohs scale. Color: reddish-brown, dark brown, or ochre. Luster: dull to earthy. Structure: fine-grained, rounded by stream or coastal erosion. Specific gravity: 3.0 - 4.3 (denser than typical silicate rocks due to iron content).
Formation & geological history
Formed through the deposition and compaction of iron-rich chemical sediments or the chemical alteration and replacement of limestone and shale by iron oxides/hydroxides over millions of years. Naturally rounded and smoothed by water transport in rivers or ocean shorelines.
Uses & applications
Historically extracted as iron ore for steel production. Water-smoothed specimens are commonly used in landscaping, aquariums, pebble art, and rock collections.
Geological facts
Ironstone rocks often form concretionary structures. Many river-tumbled ironstone pebbles contain high amounts of hematite or goethite, giving them an unusually heavy feel compared to similarly sized quartz or river stones.
Field identification & locations
Identified by its high density relative to size, dark reddish-brown hue, earthy luster, and streak test that yields a reddish-brown mark. Widely found in riverbeds, glacial deposits, and coastal beaches globally.
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