oolite

Oolite is a sedimentary rock composed mainly of ooids—tiny, nearly spherical grains typically 0.25 to 2 mm in diameter. Each ooid is a layered coating that forms around a nucleus such as a sand grain or shell fragment. When ooids cement together, the rock is termed oolitic limestone or calcarenite, depending on the proportion of carbonate mud and cement.

Formation occurs in warm, shallow marine environments where constant wave and current action keeps grains in suspension. Calcium carbonate precipitates on the surface of the nucleus in successive, concentric layers, producing the distinctive laminated ooids. Over time, diagenetic processes cement the ooids to form a coherent rock.

Oolites are found in many parts of the world. Notable oolitic limestones include those from southern England (such as Portland Stone and Bath Oolite), as well as deposits in other parts of Europe, North America, and the Caribbean. The stone is typically light-colored and granular, and has been used as a building material and decorative stone since antiquity.

Oolite is distinct from other carbonate grains such as peloids, which are non-structured and lack concentric laminae. In sedimentary rocks, classification depends on grain content and the nature of the cement, yielding terms such as oolitic limestone, oolite grainstone, and related rocks.

Other uses: Oolite is also the name of a free, open-source space simulation game inspired by Elite, unrelated to the rock.