Parisite

Parisite, a rare mineral, consisting of cerium, lanthanum, didymium and calcium fluo-carbonate, (CeF)2Ca(C03)a. It is found only as crystals, which belong to the hexagonal system and usually have the form of acute double pyramids terminated by the basal planes; the faces of the hexagonal pyramids are striated horizontally, and parallel to the basal plane there is a perfect cleavage. The crystals are hair-brown in colour and are translucent. The hardness is 41 and the specific gravity 4.36. Light which has traversed a crystal of parisite exhibits a characteristic absorption spectrum. Until recently the only known occurrence of this mineral was in the famous emerald mine at Muzo in Colombia, South America, where it was found by J. J. Paris, who re-discovered and worked the mine in the early part of the 19th century; here it is associated with emerald in a bituminous limestone of Cretaceous age (see Emerald) .

Closely allied to parisite, and indeed first described as such, is a mineral from the nepheline-syenite district of Julianehaab in south Greenland. To this the name synchysite (from Gr. alryxiioes, confounding) has been given. The crystals are rhombohedral (as distinct from hexagonal; they have the composition CeFCa(CO 3) 2, and specific gravity 2.90. At the same locality there is also found a barium-parisite, which differs from the Colombian parisite in containing barium in place of calcium, the formula being (CeF) 2 Ba(CO 3) 3: this is named cordylite on account of the club-shaped form (Kop51)Xn, a club) of its hexagonal crystals. Bastnasite is a cerium lanthanum and didymium fluo-carbonate (CeF) CO 3, from Bastnas, near Riddarhyttan, in Vestmanland, Sweden, and the Pike's Peak region in Colorado, U.S.A. (L. J. S.)