sedimentary
Limestone with Weathering Rind
Calcium Carbonate (CaCO3) - Bioclastic or Micritic Limestone
Hardness: 3 on Mohs scale (can be scratched by a penny); Color: Off-white to tan/beige; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline calcite); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.3 to 2.7
- Hardness
- 3 on Mohs scale (can be scratched by a penny)
- Color
- Off-white to tan/beige
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale (can be scratched by a penny); Color: Off-white to tan/beige; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline calcite); Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.3 to 2.7
Formation & geological history
Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris, or by chemical precipitation. This specific sample shows a clear 'weathering rind' where the outer portion has been chemically altered by exposure to air and water.
Uses & applications
Used primarily in the construction industry as road base, concrete aggregate, and for production of cement. It is also used as an agricultural soil conditioner to neutralize acidity and in the purification of iron in blast furnaces.
Geological facts
Limestone occupies about 10% of the total volume of all sedimentary rocks. It often contains fossils that help geologists date the rock layer and reconstruct ancient environments. The white portion of this sample is the result of leaching and calcite recrystallization.
Field identification & locations
Identify in the field by applying a drop of dilute hydrochloric acid (or vinegar); it will effervesce (fizz) vigorously. It is found in vast deposits globally, notably in the Great Lakes region and throughout the Midwest USA. For collectors, search for specimens with visible fossil inclusions.
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