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): "Found on several specimens forming botryoidal aggregates in quartz, associated with baryte and pseudomalachite or cornwallite from the 'old No. 2 [No. 1?] cross-cut' (Kingsbury & Hartley, MS; Hartley, 1984."