sedimentary
Ironstone Concretion (Limonite/Goethite)
Iron-rich sedimentary rock (FeOx)
Hardness: 5-5.5 on Mohs scale; Color: Dark brown, rusty orange, or black; Luster: Dull to sub-metallic; Crystal Structure: Amorphous or microcrystalline; High specific gravity (heavy for its size).
- Hardness
- 5-5
- Color
- Dark brown, rusty orange, or black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-5.5 on Mohs scale; Color: Dark brown, rusty orange, or black; Luster: Dull to sub-metallic; Crystal Structure: Amorphous or microcrystalline; High specific gravity (heavy for its size).
Formation & geological history
Formed by the precipitation of iron oxide minerals within the pore spaces of sedimentary rocks like sandstone or shale. This typically occurs in oxygenated groundwater environments during diagenesis.
Uses & applications
Historically used as an iron ore; currently used as garden decoration, for lapidary rough, or as collectible geological curiosities.
Geological facts
These are often mistaken for meteorites because of their dark, heavy appearance and rusted exterior, a phenomenon commonly called 'meteor-wrongs.'
Field identification & locations
Identify by its weight, rusty streak, and lack of internal metallic grains. Common in weathered sandstone formations and riverbeds. Collectors value specimens with unique shapes.
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