Parisite-(Ce)

Parisite
Parisite from Muzo, Vasquez-Yacopí Mining District, Boyacá Department, Colombia, size: 1.3 x 1 x .7 cm
General
Category	Carbonate
Formula (repeating unit)	Ca(Ce,La)2(CO3)3F2
IMA symbol	Pst[1]
Strunz classification	5.BD.20b
Dana classification	16a.01.05.01
Crystal system	Monoclinic
Crystal class	Domatic (m) (same H-M symbol)
Space group	Cc
Unit cell	a = 12.305 Å, b = 7.1056 Å, c = 28.2478 Å; β = 98.246°; Z = 12
Identification
Formula mass	537.24 g/mol
Color	Brown, brownish yellow, gray-yellow, grayish yellow, yellow, waxy yellow, colourless to yellow in transmitted light
Crystal habit	Acicular
Mohs scale hardness	4+1⁄2
Luster	Vitreous - greasy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	4.34
Density	4.38
References	[2][3][4]

Parisite is a rare mineral consisting of cerium, lanthanum and calcium fluoro-carbonate, Ca(Ce,La)₂(CO₃)₃F₂. Parisite is mostly parisite-(Ce), but when neodymium is present in the structure the mineral becomes parisite-(Nd).

It is found only as crystals, which belong to the trigonal or monoclinic pseudo-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 color and are translucent. The hardness is 4.5 and the specific gravity is 4.36. Light which has traversed a crystal of parisite exhibits a characteristic absorption spectrum.

At first, 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 rediscovered 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.

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 has been given. The crystals are rhombohedral (as distinct from hexagonal; they have the composition CeFCa(CO₃)₂, and specific gravity of 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 of its hexagonal crystals. Bastnasite is a cerium lanthanum and neodymium fluoro-carbonate (CeF)CO₃, from Bastnas, near Riddarhyttan, in Vestmanland, Sweden, and the Pikes Peak region in Colorado, United States.