Oolitic Limestone

Physical Properties

Hardness: 3-4 (Mohs scale); Color: Tan, cream, or light grey with dark iron-stained patches; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in individual grains; Texture: Oolitic (spherical grains called ooids).

Formation & Geological History

Formed in warm, shallow, supersaturated marine environments. Waves roll sand grains or shell fragments, causing calcium carbonate to precipitate in concentric layers around them. Most date from the Jurassic or Carboniferous periods.

Uses & Applications

Used in construction as a building stone (Portland stone), in the manufacture of lime, and as an ornamental stone in gardens and sculptures.

Geological Facts

The name 'oolite' comes from the Greek word 'oon' for egg, because the texture resembles fish roe. Major landmarks like the Empire State Building are faced with Indiana Oolitic Limestone.

Field Identification & Locations

Identify by the presence of small, spherical, sand-sized grains (ooids) that look like tiny pearls. It will effervesce (fizz) when in contact with dilute hydrochloric acid. Commonly found in areas that were once shallow tropical seas.

Identified on: 5/7/2026

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