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 crystals are long narrow thin plates without for the most part any terminal faces and when measured gave angles consistent with the supposition that they are crystals of paralaurionite elongated along the symmetry-axis and twinned about a(100) with the faces of a large and those of c(001) small. [...] There is an excellent cleavage parallel to c(001). Indications of other faces in the zone a c were observed, and it is probable that h(201) is present on some crystals as a very narrow face. The important face m(110) mentioned by Herbert Smith was not observed, but a face making an angle of 24°24' with a was found instead. Simple indices cannot be assigned to this face ((510) would correspond to an angle from a of 25°38') and it is probable that it is an accidental face produced where one crystal has come in contact with another.[...]
