oolite

noun2

1. •
   A rock consisting of spherical grains within a mineral cortex accreted around a nucleus, often of quartz grains.

   • Here and there are beds of oolites, for example, made of little rounded grains – like millet seed – that form only in agitated warm waters, such as you might find off the Bahamas today. — 2004
2. •
   (rare) An ooid or oolith.