di·o·rite 
(dīə-rīt′)
(dīə-rīt′)n.
Any of various dark, granite-textured, crystalline rocks rich in plagioclase feldspar and having little quartz.
[French, from Greek diorizein, to distinguish : dia-, apart, between; see DIA- + horizein, to divide, limit; see HORIZON.]
di′o·ritic (-rĭtĭk) adj.