sedimentary
Limestone with Fossil Imprints
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 3 (Mohs scale); Color: light grey to tan; Luster: earthy/dull; Structure: fine-grained microcrystalline with fossiliferous indentations; Cleavage: none (conchoidal fracture).
- Hardness
- 3 (Mohs scale)
- Color
- light grey to tan
- Luster
- earthy/dull
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Physical properties
Hardness: 3 (Mohs scale); Color: light grey to tan; Luster: earthy/dull; Structure: fine-grained microcrystalline with fossiliferous indentations; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed in shallow marine environments from the accumulation of shell, coral, and algal debris. The marks are tectonic or biological imprints (possibly shell fragments or 'chicken track' impressions) weathered into the stone over millions of years.
Uses & applications
Used extensively in the manufacture of cement, as a building stone (limestone blocks), in agriculture to neutralize soil acidity, and as a crushed stone for road bases.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains fossils that help geologists date the rock layer and identify ancient environments.
Field identification & locations
Identify in the field by its softness (can be scratched by a copper penny) and its reaction to weak acid (it will fizz or effervesce). Commonly found in ancient sea beds and karst landscapes.
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