sedimentary
Fossiliferous Limestone
Biogenic Limestone (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, tan, or grey with visible fossil imprints; Luster: Dull to earthy; Crystal structure: Trigonal/Hexagonal (calcite matrix); Specific gravity: 2.3 to 2.7.
- Hardness
- 3 on Mohs scale
- Color
- Cream, tan, or grey with visible fossil imprints
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, tan, or grey with visible fossil imprints; Luster: Dull to earthy; Crystal structure: Trigonal/Hexagonal (calcite matrix); Specific gravity: 2.3 to 2.7.
Formation & geological history
Formed in marine environments as biological debris (shells, coral, and fragments) accumulates on the ocean floor and is buried and lithified. Many available specimens date from the Paleozoic or Mesozoic eras.
Uses & applications
Primarily used in construction (crushed stone, road base, or dimension stone), cement manufacturing, and as a soil conditioner in agriculture. High-quality fossil specimens are used for teaching and collecting.
Geological facts
This specimen contains a visible fossil mold or impression, likely of a marine invertebrate like a crinoid stem or shell fragment. Limestone makes up about 10% of the total volume of all sedimentary rocks.
Field identification & locations
Identify in the field by its light color, grainy texture, and the 'fizz test' (reacts to dilute hydrochloric acid). Common in areas that were once ancient sea beds, such as the Midwest US or the Jurassic Coast in the UK.
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