Oolitic Limestone

Physical Properties

Hardness: 3-4 (Mohs); Color: Grey, tan, or white; Luster: Dull/Earthy; Crystal structure: Amorphous/Microcrystalline; Composed of small spherical grains called ooids.

Formation & Geological History

Formed in warm, shallow, supersaturated marine waters. Ooids form when calcium carbonate precipitates around a nucleus (like a shell fragment) and is rolled by wave action. Often dating from the Jurassic or Carboniferous periods.

Uses & Applications

Used as a building material (Portland stone), in the manufacture of lime, as a flux in steel making, and in road construction. Smaller pieces are common in geological collections.

Geological Facts

The name comes from the Ancient Greek word 'oon' for egg, because it looks like fish roe. Much of the architecture in Washington D.C. and many cathedrals in Europe are built from oolitic limestone.

Field Identification & Locations

Identify in the field by looking for the characteristic 'sand-grain' or 'caviar' texture. It will react and fizz strongly when exposed to dilute hydrochloric acid (acid test). Commonly found in the UK (Cotswolds), USA (Indiana, Florida), and the Bahamas.

Identified on: 4/22/2026

Mode: Standard