sedimentary
Ironstone (likely Limonite or Goethite)
Ferruginous sedimentary rock (FeO(OH)·nH2O)
Hardness: 4-5.5 (Mohs scale); Color: Dark brown to yellowish-brown; Luster: Dull, earthy to sub-metallic; Crystal Structure: Amorphous or microcrystalline; Specific Gravity: 2.7–4.3.
- Hardness
- 4-5
- Color
- Dark brown to yellowish-brown
- Luster
- Dull, earthy to sub-metallic
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Physical properties
Hardness: 4-5.5 (Mohs scale); Color: Dark brown to yellowish-brown; Luster: Dull, earthy to sub-metallic; Crystal Structure: Amorphous or microcrystalline; Specific Gravity: 2.7–4.3.
Formation & geological history
Formed through the chemical precipitation of iron oxides in sedimentary environments such as marine, lacustrine, or bog settings. Often these specimens represent iron-rich nodules or weathered 'concretions'.
Uses & applications
Historically used as a low-grade iron ore. Today, it is primarily used as decorative garden stone, in road construction (base material), or for lapidary work like making cabochons.
Geological facts
Ironstone was a critical driver of the Industrial Revolution in regions like Great Britain, provided the iron necessary for early steel production. The distinct ochre color comes from the oxidation (rusting) of iron minerals.
Field identification & locations
Identify in the field by its high weight (density) compared to surrounding rocks and its characteristic rusty yellow-brown streak when scratched on unglazed porcelain. Commonly found in riverbeds or eroded sedimentary layers.
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