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!
"Andersine is the most abundant mineral in the cavities, generally forming simple, thin, tabular crystals up to 2 x 1 0.3 cm. They are greyish in hand specimen, but are nearly transparent when viewed under the microscope. The crystals are flattened parallel to (010) and may be slightly elongated parallel to the c axis. Occasional hollowed terminations are observed. Optically, the crystals are twinned on the Carlsbad and Albite laws and show only slight concentric zonation. The Portland occurrence is of some significance as free-standing crystals are rare."
Portland Harbour Trust Quarry, Cape Sir William Grant, Portland, Glenelg Shire, Victoria, Australia