an·or·thite 
(ăn-ôrthīt)
(ăn-ôrthīt)n.
A white to gray variety of plagioclase feldspar that contains a high proportion of calcium to sodium and occurs in alkaline igneous rocks such as gabbro and anorthosite.
[From Greek an-, not; see A-1 + orthos, straight (from its oblique crystals).]
an′or·thitic (-thĭtĭk) adj.