Mid 19th century; earliest use found in James Dana (1813–1895), geologist, zoologist, and teacher. From French phtanite from ancient Greek ϕθάνειν to anticipate (of unknown origin) + French -ite, so named ‘because its thick schistoid texture and argillaceous character seem to announce beforehand its passage into schist’ (‘parce que sa texture schistoïde épaisse et son caractère argileux semblent annoncer d'avance son passage au schiste’).