sedimentary
Oolite (Ooid Limestone)
Ooidal Limestone (comprised of CaCO3)
AI-generated identification · may be incorrectHardness: 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
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Physical properties
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.
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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