Oolitic Limestone

Hardness: 3-4 Mohs; Color: Tan, cream, or light gray; Luster: Dull to earthy; Texture: Granular (composed of tiny spherical ooids); Cleavage: Uneven; Specific Gravity: 2.5-2.7

Formed in warm, shallow, agitated marine environments where calcium carbonate precipitates around a nucleus (like a sand grain or shell fragment) through wave action, creating spherical 'ooids'. Accumulation and cementation occur over millions of years, often dating from the Jurassic to the Carboniferous periods.

Extensively used as a high-quality building stone (dimension stone), in the manufacture of lime, concrete production, as an agricultural soil conditioner, and occasionally for sculpting.

The ooids resemble small fish eggs, which is why it is historically called 'egg stone'. Many famous buildings, including the Pentagon and much of the White House, are constructed using Indiana Limestone, which is a type of oolitic limestone.

Identify in the field by looking for the distinctive 'sandpaper' texture or small spherical grains visible under a hand lens. It will react and fizz strongly when a drop of dilute hydrochloric acid is applied. Commonly found in areas that were formerly shallow inland seas, such as Indiana (USA), Florida (USA), and the Cotswolds (UK).