a soft, orthorhombic mineral, SrSO, that is the chief ore of strontium; strontium sulfate
See celestite in American Heritage Dictionary 4
(sĕlˈĭ-stītˌ, sə-lĕsˈtītˌ)
noun
A white, red-brown, orange, or light blue principal strontium ore, essentially strontium sulfate, SrSO4, found in sedimentary rock. Also called celestine.