sedimentary

Oolite (Ooid)

Oolitic Limestone (chiefly CaCO3)

Hardness: 3-4 Mohs; Color: Cream, tan, or white; Luster: Earthy to pearly; Structure: Spherical grains (ooids) composed of concentric layers; Cleavage: None (grains are rounded)

Hardness: 3-4 Mohs
Color: Cream, tan, or white
Luster: Earthy to pearly

Identified June 6, 2026More sedimentary →

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Physical properties

Hardness: 3-4 Mohs; Color: Cream, tan, or white; Luster: Earthy to pearly; Structure: Spherical grains (ooids) composed of concentric layers; Cleavage: None (grains are rounded)

Formation & geological history

Formed in warm, shallow, oversaturated marine waters where calcium carbonate precipitates around a nucleus, such as a shell fragment or sand grain, through wave action.

Uses & applications

Used in the manufacturing of lime, as a flux in steel production, as building stone, and occasionally as decorative gravel or for educational collecting.

Geological facts

The name comes from the Ancient Greek word 'oion' for egg, because the clusters of ooids look like fish roe. Major formations exist in the Bahamas and the Great Salt Lake.

Field identification & locations

Identify by its distinct spheroidal shape and concentric internal layering if broken. Commonly found in tropical marine environments or ancient seafloor deposits.