sedimentary
Ironstone Concretion / Limonite Node
Goethite / Limonite (FeO(OH)·nH2O)
Hardness: 4-5.5 (Mohs scale); Color: Rusty brown, yellowish-brown, ochre; Luster: Dull, earthy, or sub-metallic; Structure: Often rounded, botryoidal, or nodular; Specific Gravity: 2.7-4.3.
- Hardness
- 4-5
- Color
- Rusty brown, yellowish-brown, ochre
- Luster
- Dull, earthy, or sub-metallic
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Physical properties
Hardness: 4-5.5 (Mohs scale); Color: Rusty brown, yellowish-brown, ochre; Luster: Dull, earthy, or sub-metallic; Structure: Often rounded, botryoidal, or nodular; Specific Gravity: 2.7-4.3.
Formation & geological history
Formed by the precipitation of iron oxide minerals within sedimentary layers, often around a nucleus like a leaf, shell, or pebble. They typically form during diagenesis in environments like bogs, lakes, or shallow marine settings.
Uses & applications
Historically used as a low-grade iron ore. Today, used primarily as a decorative stone in landscaping, a source of natural pigments (ochre), or as a geological curiosity for collectors.
Geological facts
These nodules are often mistaken for meteorites due to their heavy weight and dark, weathered appearance. Some hollow ironstone concretions are known as 'rattle stones' or 'etites' because smaller stones loose inside can rattle when shaken.
Field identification & locations
Identify in the field by its distinct rusty color, high density compared to surrounding rocks, and common spherical or oval shape. Found globally in sandstone and shale formations. Collectors should look for signs of internal fossils or hollow cavities.
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