sedimentary
Gray Limestone
Calcite-rich Sedimentary Rock (CaCO3)
Hardness: 3-4 (Mohs scale), Color: light to dark gray, Luster: dull to earthy, Crystal Structure: Trigonal/Microcrystalline, Cleavage: none, Specific Gravity: 2.3-2.7
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Physical properties
Hardness: 3-4 (Mohs scale), Color: light to dark gray, Luster: dull to earthy, Crystal Structure: Trigonal/Microcrystalline, Cleavage: none, Specific Gravity: 2.3-2.7
Formation & geological history
Formed through the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. Can also form by the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Primary source of lime for cement, used as a building stone, crushed for road base, used as a soil conditioner in agriculture, and in the manufacturing of glass.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed by the dissolution of limestone by slightly acidic groundwater.
Field identification & locations
Identify in the field by its gray color and the 'acid test' where it will fizz (effervesce) when a drop of 10% hydrochloric acid is applied. Very common globally.
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