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!
"The biotite from Bastogne, particularly poor in potassium and rich in ferric iron and water, shows an enrichment in NH4+ (Darimont et al., 1988). An alteration of the mineral is evident by whitening and a variation in the optical axes angle. The X-ray powder diagram reveals a peak at 14Å, which could indicate a vermiculitisation phenomenon." (Hatert et al, 2002)
