'plagioclase-rich' originates from Modern English as a compound of 'plagioclase' and the suffix/word element 'rich'. 'Plagioclase' itself was adopted into English from Neo-Latin/Greek-derived scientific formation, while 'rich' traces to Old English 'rice'/'ric' meaning 'powerful, abundant'.

'Plagioclase' was coined in mineralogical/chemical nomenclature in the 19th century from Neo-Latin (from Greek elements 'plagios' and 'klasis'), and later combined with the English adjective 'rich' to form the compound 'plagioclase-rich' in geological descriptions; 'rich' evolved from Old English 'rice' (Germanic).

Initially the component terms referred to 'oblique'/'breaking' (Greek roots used to name the mineral group) and 'abundant/powerful' (Old English for 'rich'); combined as 'plagioclase-rich' the meaning became the straightforward descriptive sense 'abundant in plagioclase', which has remained stable in geological usage.