PARISITE  , a rare

mineral, consisting of cerium, lanthanum, didymium and calcium fluo-carbonate, (CeF)2Ca(COs), . 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. uvryxuons, confounding) has been given . The crystals are rhombohedral (as distinct from hexagonal; they have the composition CeFCa(CO3)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)2Ba(CO3)3: this is named cordylite on account of the club-shaped form (KOpbbXtl) a club) of its hexagonal crystals .

Bastnasite is a cerium lanthanum and didymium fluo-carbonate (CeF)COa, from Bastnas, near Riddarhyttan, in Vestmanland,

Sweden, and the Pike's Peak region in Colorado, U.S.A . (L . J .