I have seen this material before turn up in old East Coast collections and usually pegged as of little value because they tend to look like ugly brown lumps. This piece, however, is a raging beauty queen for the species in that it has some aesthetics of geometry at least. It is sharply doubly-terminated, and not cracked and pasty as these tend to get. According to Mindat.org: A zincian manganoan variety of augite, a clinopyroxene. Originally described from Passaic Pit (Marshall Mine; Passaic Mine), Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey. Ex George Elling's well-known Collection