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): "As sprays of incomplete, bladed, crystals (< 10mm) in joints in a gossany matrix (Kingsbury Collection, BM(NH)); listed by Hartley (1984)."