Wurtzite is a relatively uncommon zinc, iron sulfide. It usually occurs as massive ore or as banded, botryoidal crusts. It is very rare as displayed in the sharp, hexagonal, stacked, tabular crystals on massive wurtzite matrix on this superb thumbnail from the Dick Jones Collection. The lustrous crystals have a nice purple iridescence to them. This classic, old-time specimen, dating to the 1960s or 1970s, is from the Siglo XX Mine of Bolivia.