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!
Cooper & Stanley (1990): "'In one of the branches of the gill, a quartz vein, bearing either manganite or pyrolusite stands like a wall on the fellside...' (Davidson & Thomson, 1951: 140)."