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!
"Not seen" by Schooner (1955). Schairer (1931) seems to be the source of all later repetition, and he said it was found "very rarely" in Portland. This generic reference probably means the much older Pelton Quarry where it is well known.