sedimentary

Limestone (specifically Fossiliferous or Crinoidal Limestone)

Calcium Carbonate (CaCO3) - Calcite Rock

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale (can be scratched by a copper penny or knife); Color: Light to dark grey, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal/Hexagonal (microcrystalline calcite); Cleavage: Perfect rhombohedral in calcite crystals, though usually massive; Specific Gravity: 2.3 to 2.7.

Color: Light to dark grey, tan, or white
Luster: Dull to earthy

Identified March 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of organic debris such as shell fragments, coral, or calcium carbonate precipitate in warm, shallow marine environments. Most common specimens date from the Paleozoic or Mesozoic eras (spanning over 500 million years).

Uses & applications

Extensively used as a construction material (aggregate, road base), in the production of cement and lime, as a soil conditioner in agriculture, and for architectural facade stone. Pure varieties are used in toothpaste and paper production.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Landscapes formed of limestone, known as karst, are famous for caves, sinkholes, and underground drainage systems. The Great Pyramid of Giza was originally encased in white Tura limestone.

Field identification & locations

Identify in the field by applying a drop of white vinegar (acid test); it will effervesce (fizz) as it releases carbon dioxide. Look for visible shell fragments or fossils. It is commonly found in regions that were once ancient seabed, such as the Midwestern United States, parts of Europe, and China.