sedimentary
Ooids (Oolites)
Ooids (composed of Calcium Carbonate / CaCO3)
Hardness: 3 (Mohs scale), Color: White, gray, or tan, Luster: Dull to pearly, structure: Spherical to egg-shaped grains with concentric internal layering, Cleavage: None (grains are aggregates).
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Physical properties
Hardness: 3 (Mohs scale), Color: White, gray, or tan, Luster: Dull to pearly, structure: Spherical to egg-shaped grains with concentric internal layering, Cleavage: None (grains are aggregates).
Formation & geological history
Formed through the chemical precipitation of calcium carbonate around a nucleus (such as a grain of sand or shell fragment) in warm, shallow, agitated marine waters. Occur predominantly in Phanerozoic era strata.
Uses & applications
Used as building stone (Oolitic Limestone), in the production of lime and cement, as flux in steel making, and as a calcium supplement in agriculture.
Geological facts
The name comes from the Greek word 'oion' for egg. Famous examples include the Portland Stone used in St. Paul's Cathedral and the oolitic sands of the Bahamas.
Field identification & locations
Identify by their distinct small, round, 'fish-egg' appearance (usually less than 2mm). Found in current environments like the Persian Gulf or Bahamian banks, and in ancient limestone outcrops in the Midwestern US and UK.
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