sedimentary
Limonite Geode / Ironstone Concretion with Quartz
Limonite with Quartz (FeO(OH)·nH2O + SiO2)
Hardness: 4-5.5 (limonite shell), 7 (quartz crystals); Color: Dark brown to ochre; Luster: Dull/earthy exterior, vitreous interior; Crystal structure: Amorphous shell, trigonal quartz crystals inside.
- Hardness
- 4-5
- Color
- Dark brown to ochre
- Luster
- Dull/earthy exterior, vitreous interior
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Physical properties
Hardness: 4-5.5 (limonite shell), 7 (quartz crystals); Color: Dark brown to ochre; Luster: Dull/earthy exterior, vitreous interior; Crystal structure: Amorphous shell, trigonal quartz crystals inside.
Formation & geological history
Formed via the precipitation of iron oxides from groundwater within sedimentary layers, often creating a hollow concretion which later hosts secondary mineral growth like quartz.
Uses & applications
Geological collecting, educational specimens, and occasionally as a minor iron ore.
Geological facts
These are often called 'rattle stones' or 'etites' if the internal crystals break loose and shake inside the hollow cavity.
Field identification & locations
Identified by its heavy iron-rich outer shell and characteristic vugs or hollows often filled with small crystals. Commonly found in areas with iron-rich sandstone or clay deposits.
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