a light-colored, hard, crystalline pyroxene, CaMg(SiO), calcium magnesium silicate, found in some limestones and metamorphic rocks and sometimes used as a gem
See diopside in American Heritage Dictionary 4
(dī-ŏpˈsīdˌ)
noun
A light green, monoclinic pyroxene mineral, CaMgSi2O6, used as a gemstone and refractory.