sedimentary
Goethite / Limonite Concretion
Iron Hydroxide Oxide (FeO(OH))
Hardness: 5-5.5; Color: Dark brown to black with rusty orange/yellow interiors; Luster: Dull to sub-metallic; Structure: Massively amorphous or cryptocrystalline; Cleavage: None; Specific Gravity: 3.3-4.3
- Hardness
- 5-5
- Color
- Dark brown to black with rusty orange/yellow interiors
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-5.5; Color: Dark brown to black with rusty orange/yellow interiors; Luster: Dull to sub-metallic; Structure: Massively amorphous or cryptocrystalline; Cleavage: None; Specific Gravity: 3.3-4.3
Formation & geological history
Formed by the weathering of iron-rich sedimentary rocks or the precipitation of iron from groundwater in an oxidizing environment. They often form as nodules around a core material.
Uses & applications
Primarily collected as geological specimens. Larger deposits are historically used as low-grade iron ore. Goethite is also used as a yellow ochre pigment.
Geological facts
These stones are often mistaken for meteorites due to their dark, bumpy or pitted surfaces, which look like 'regmaglypts' but are actually the result of chemical weathering or botryoidal growth patterns.
Field identification & locations
Check for a yellow-brown streak by rubbing against white ceramic. Look for a 'rusty' interior when broken. Often found in soil, riverbeds, or limestone-rich areas where iron minerals are present.
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