ooidal vs spherical

ooidal

adj
  • Egg-shaped. 

  • Oolitic. 

spherical

adj
  • Shaped like a sphere. 

  • Of or relating to the heavenly orbs, or to the sphere or spheres in which, according to ancient astronomy and astrology, they were set. 

  • Of a coordinate system, specifying the location of a point in a plane by using a radius and two angles. 

  • Of, or pertaining to, spheres. 

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