idocrase /ˈīdəkrās, ˈaɪdəkreɪs 
/ ▸ noun a mineral consisting of a silicate of calcium, magnesium, and aluminum, occurring typically as dark green to brown prisms in metamorphosed limestone.
– ORIGIN early 19th century : from Greek eidos ‘form’ + krasis ‘mixture’.
EnglishOxford New American Dictionary
