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!
Russell and Hutchinson (1927): "The crystals of laurionite are colourless and translucent and bladed in form, attaining a length of 4 mm.[...] The following forms are present: b(010), m(110), n(120), d(012), and the prominent but somewhat doubtful form p(141). [...] The faces as a whole appeared to be etched and afford multiple images, with the exception of m(110) which gives good reflections. As in the case of the Laurion crystals the faces of b(010) are striated parallel to their intersection with the pyramid p(141), the latter being possibly a vicinal form as suggested by Dr. Herbert Smith. The edges formed by the intersection of the faces p(141) are always more or less curved, thus giving rise to the bladed form. No interference-figure can be seen looking through (010). The crystals when powdered are partially soluble in boiling water. The presence of lead and chlorine was determined. Of the three associated minerals, laurionite, phosgenite, and anglesite, the laurionite appears to have been the last formed, and partially invests the other two."
