Taranakite
Taranakite crystallizes in the hexagonal system , and is noted as having the longest crystallographic axis of any known mineral: the "c"-axis of the taranakite unit cell is 9 . 505 nanometers long . 
<triplet> hexagonal system <subj> crystallographic axis <obj> subclass of <triplet> "c" <subj> crystallographic axis <obj> subclass of