Vote for your favorite mineral in #MinCup26! - Sphalerite vs. Anorthite Both zinc ore Sphalerite and calcium plagioclase feldspar Anorthite have perfect cleavage that will split cleanly if you hit them with a hammer, but only one can claim a larger split of your votes!
Kingsbury reference. Cooper & Stanley (1990): "A single specimen from the upper level dump (Kingsbury Collection, BM(NH) has a blue-grey encrustation of plumbogummite partly epimorphous after pyromorphite. No other specimens have been located."