oolith

From Latin oolithus, from Ancient Greek ᾠο- (ōio-, “oo-”) + λίθος (líthos, “stone”), corresponding to oo- +‎ -lith.

• (UK) IPA^(key): /ˈəʊəlɪθ/

oolith (plural ooliths)

1. (geology) A spherical granule of which oolite is composed, formed by concentric accretion of thin layers of a mineral around a core. Calcium carbonate (limestone) is the most common mineral that forms ooliths, but they may also form from other minerals such as dolomite and silica.
2. (rare) Oolite.

Glossary of Geology, 2nd Edition, American Geological Institute

• tholoi