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!
'Brewsterite Subgroup' (not an IMA approved species)
Comments:
Cooper & Stanley (1990): "The 'brewsterite' recorded by Hall (1868) as an associate of tenorite and chalcopyrite is unlikely to be the zeolitic brewsterite (of Brooke) as assumed by Young (1987). It is more likely to be the 'brewsterite' listed by Branston (1910) and Postlethwaite (1913) as 'protoxide of copper'. Although the latter is a synonym of cuprite, the name brewsterite in this context does not appear in any standard mineralogy or synonymy known to the authors and the precise definition of the term appears to be lost."
