ooid vs ooidal

ooid

adj
  • Shaped like an egg; ovoid; ovate. 

noun
  • A small calcium carbonate or iron coated grain found on the seafloor. 

ooidal

adj
  • Egg-shaped. 

  • Oolitic. 

How often have the words ooid and ooidal occurred in a corpus of books? (source: Google Ngram Viewer )