'anorthosite-free' is a modern English compound formed from the noun 'anorthosite' and the suffix '-free' (meaning 'without'). 'anorthosite' itself comes from New Latin 'anorthosite' (a rock name derived from the mineral name 'anorthite'), where the Greek prefix 'an-' meant 'not' and 'orthos' meant 'straight/right' (elements used in mineral naming).

'anorthosite' entered geological usage via New Latin in the 19th century (formed from 'anorthite' + the rock-forming suffix '-osite'), and the adhesive English suffix '-free' derives from Old English 'frēo' and later developed as a productive suffix in Modern English compounds meaning 'without'. The compound 'anorthosite-free' is therefore a straightforward, modern lexical formation combining these elements.

The individual parts maintained their basic senses: 'anorthosite' denotes the specific rock type, while 'free' originally meant 'not enslaved/exempt' and has extended to a compound suffix meaning 'without'. Together they now mean 'without anorthosite'.