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. Kingsbury and Hartley (1958): "in oxidized vein-material from the northernmost of the two old cross-cuts near the head of the gill; occurs in small brown rhombohedral crystals, some of them altering to 'limonite', with arsenates."