sedimentary
Limestone (Weathered / Limonite-stained)
Sedimentary carbonate rock (CaCO3)
Hardness: 3 on the Mohs scale. Color: Brownish-orange due to iron oxide (limonite) staining on the exterior. Luster: Dull to earthy. Crystal structure: Microcrystalline or cryptocrystalline calcite matrix. Cleavage: Good rhombohedral cleavage in pure calcite, though often obscured in weathered hand specimens.…
- Hardness
- 3 on the Mohs scale
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on the Mohs scale. Color: Brownish-orange due to iron oxide (limonite) staining on the exterior. Luster: Dull to earthy. Crystal structure: Microcrystalline or cryptocrystalline calcite matrix. Cleavage: Good rhombohedral cleavage in pure calcite, though often obscured in weathered hand specimens. Specific gravity: 2.7 to 2.9.
Formation & geological history
Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris, or via chemical precipitation of calcium carbonate from water. Subjected to subaerial weathering, oxidation, and iron-staining over geological time.
Uses & applications
Used in construction as crushed stone for road base, aggregate in concrete, production of lime and cement, and in agriculture for soil neutralization.
Geological facts
Limestone often contains fossils of ancient marine organisms. Weathered surface samples like this commonly take on a characteristic rusty brown coating due to percolating groundwater carrying iron minerals.
Field identification & locations
Easily identifiable in the field by its moderate hardness (can be scratched with a knife or nail) and vigorous fizzing/effervescence when a drop of dilute hydrochloric acid is applied due to the release of carbon dioxide.
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