sedimentary
Limestone (Concretionary or Tufa)
Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs scale), Color: tan, buff, or light brown, Luster: dull to earthy, Crystal Structure: often microcrystalline (calcite), Cleavage: none in bulk form, Specific Gravity: 2.3-2.7
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Physical properties
Hardness: 3-4 (Mohs scale), Color: tan, buff, or light brown, Luster: dull to earthy, Crystal Structure: often microcrystalline (calcite), Cleavage: none in bulk form, Specific Gravity: 2.3-2.7
Formation & geological history
Formed through the precipitation of calcium carbonate from mineral-rich waters, often around organic debris or within sedimentary beds. These rocks can range from tens of thousands to millions of years old depending on the local geology.
Uses & applications
Commonly used as decorative garden stone, construction aggregate, and in the production of cement and lime for agriculture.
Geological facts
The hollow center suggest it may have been a concretion where the softer core weathered away, or a 'Holey Stone' naturally eroded by water or biological activity.
Field identification & locations
Identify in the field by its reaction (fizzing) with diluted hydrochloric acid. Look for porous textures and sedimentary layering. Commonly found in karst landscapes and limestone quarries.
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