The word "quartz" is derived from the German word "Quarz" and its Middle High German ancestor "twarc", which probably originated in Slavic, cf.
The Ancient Greeks referred to quartz as κρύσταλλος (krustallos) derived from the Ancient Greek κρύος (kruos) meaning "icy cold", because some philosophers (including Theophrastus) apparently believed the mineral to be a form of supercooled ice [REF].