sedimentary

Oolite (Ooid Limestone)

Ooidal Limestone (comprised of CaCO3)

Hardness: 3 (Mohs scale); Color: Typically white, grey, or tan; Luster: Dull/Earthy; Crystal Structure: Orthorhombic or Trigonal (Aragonite/Calcite); Cleavage: Perfect rhombohedral in individual crystals; Specific Gravity: 2.7.

Hardness: 3 (Mohs scale)
Color: Typically white, grey, or tan
Luster: Dull/Earthy

Identified January 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in warm, shallow, supersaturated marine waters. Wave action rolls sand grains or shell fragments, allowing calcium carbonate to precipitate in concentric layers (concentric accretion). Found in environments like the Bahamas or the Great Salt Lake.

Uses & applications

Used as building stone, as a flux in steel making, in the production of lime and cement, and occasionally as an aggregate in road construction.

Geological facts

The word 'Oolite' comes from the Greek 'oon' for egg, because the grains look like fish roe. When individual ooids are larger than 2mm, they are called pisoids, and the rock is known as pisolite.

Field identification & locations

Field identification: Look for small (0.25 to 2 mm), spherical, seed-like grains. It will effervesce (fizz) vigorously when in contact with dilute hydrochloric acid. It is commonly found in Jurassic-aged limestone formations throughout Europe and the American Midwest.

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