sedimentary
Limonite Concretion
Goethite-Limonite (FeO(OH)·nH2O)
Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
- Hardness
- 4
- Color
- Yellowish-brown to dark brown
- Luster
- Dull or earthy
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Physical properties
Hardness: 4.0-5.5 (Mohs scale); Color: Yellowish-brown to dark brown; Luster: Dull or earthy; Crystal structure: Amorphous; Cleavage: None; Specific Gravity: 2.7-4.3
Formation & geological history
Formed via chemical precipitation of iron-rich minerals in sedimentary rock layers, often around a nucleus like a leaf, shell, or fossil. These often accumulate in boggy environments or weathering zones of iron-bearing rocks.
Uses & applications
Historically used as a low-grade iron ore (limonite) and as a pigment (ochre); today primarily used as decorative garden stones or for geological study.
Geological facts
Often called 'Moqui marbles' or 'shaman stones' when found in specific round shapes, these were once thought to be meteorites or mystical objects due to their unusual spherical forms.
Field identification & locations
Identified by its heavy weight relative to size, brownish-yellow streak, and spherical or nodular shape. Common in sandstone formations and dry desert washes.
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