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): "From the upper west level dumps (Hartley, 1984); specimens in the Kingsbury Collection, BM(NH), show 1-2mm crystals with linarite."