Oolite (
egg stone) is a
sedimentary rock formed from
ooids, spherical grains composed of concentric layers. The name derives from the
Ancient Greek word
ᾠόν for
egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm;
rocks composed of ooids larger than 2 mm are called
pisolites. The term
oolith can refer to oolite or individual ooids.