Synchysite-(Ce)

Ca(Ce, La)(CO3)2 F
c 2001-2005 Mineral Data Publishing, version 1

Crystal Data: Monoclinic, pseudohexagonal. Point Group: 2/m. Crystals are commonly
acute pyramidal [using pseudohexagonal indices] {1010} to tabular and striated k {0001},
but oscillatory and sceptered due to syntactic intergrowths k {0001} with bastnäsite-(Ce),parisite-(Ce), röntgenite-(Ce), cordylite, to 6 cm. Twinning: On {0001}, may be lamellar.
Physical Properties: Fracture: Subconchoidal to splintery.
Hardness = 4.5 D(meas.) = 3.90 D(calc.) = 3.88

Tenacity: Brittle.

Optical Properties: Translucent. Color: Wax-yellow, brown, grayish yellow; colorless to paleyellow in transmitted light. Luster: Vitreous to subadamantine, may be greasy.
Optical Class: Uniaxial (+). Pleochroism: Weak. Absorption: O < E. ω = 1.674  = 1.770
Cell Data: Space Group: C2/c. a = 12.329(2)β = 102.68(1)◦ Z = 12b = 7.110(1)c = 18.741(2)X-ray Powder Pattern: Predazzo, Italy.
3.55 (100), 2.80 (100), 9.1 (60), 4.53 (50), 2.06 (50), 1.934 (50), 3.32 (40)Chemistry:
CO2SiO2Y2 O3
La2 O3(1)[27.95]
0.14
0.45
9.96

Ce2 O3Pr2 O3
Nd2 O3
Sm2 O3(1)
22.34
2.27
12.73
1.79

Gd2 O3CaO
F−O = F2(1)
1.27
18.14
[5.73]
2.41

Total[100.36](1) Trimouns talc deposit, France; by electron microprobe, average of ten points, CO2 andF calculated from stoichiometry; corresponds to Ca1.02 (Ce0.43 La0.24 Nd0.19 Pr0.05 Sm0.03 Gd0.02
Y0.01 )Σ=0.97 (CO3 )2 F. (2) Mont Saint-Hilaire, Canada; analysis not given, stated to correspond to
Ca0.94 (Ce0.62 La0.32 Y0.02 Th0.01 Eu0.01 )Σ=0.98 (CO3 )2 F0.64 .
Occurrence:

An uncommon hydrothermal accessory mineral in granites and alkalic syenites.

Association: Astrophyllite, catapleiite, neptunite, epididymite, elpidite, cordylite, fluorite,
rhodochrosite, polylithionite, aegirine, microcline, albite (Narssârssuk, Greenland); ewaldite,belovite-(Ce), fluorite, nenadkevichite, ancylite-(Ce), kukharenkoite-(Ce), mckelveyite-(Y),burbankite, calcite, barite, orthoclase (Khibiny massif, Russia).
Distribution: In Greenland, very large crystals from Narssârssuk, and in the Ilı́maussaq
intrusion. At Holmestrand, Norway. In the Valle de Arán, Lerida Province, Spain. In Italy, fromPredazzo, Trentino-Alto Adige, and on the east flank of Pizzo Cervandone, Alpe Devero, Vald’Aosta, Piedmont. In Switzerland, from Piz Blas, Val Nalps, and at La Bianca, Val Casatscha,
Grisons; on the west flank of Cherbadung [Pizzo Cervandone], Binntal, Valais; with manyother minor occurrences. In the Kaiserer and Lohningbruch quarries, Rauris Valley, Salzburg,Austria. In the Trimouns talc deposit, six km northeast of Luzenac, Ariège, France. In Russia,
rock-forming in the Khibiny massif, Kola Peninsula. From the Lueshe carbonatite, 150 km
north of Goma, Kivu Province, Congo (Zaire). In Canada, from Mont Saint-Hilaire and at
Saint-Amable, Quebec. From Mt. Weld, 34 km south of Laverton, Western Australia. Increasinglyrecognized from additional localities.
Name:cerium.

From the Greek for confounding, as originally thought to be parisite, and dominant

Type Material:

University of Copenhagen, Copenhagen, Denmark.

References: (1) Palache, C., H. Berman, and C. Frondel (1951) Dana’s system of mineralogy,(7th edition), v. II, 287–289. (2) Wang, L., Y. Ni, J.M. Hughes, P. Bayliss, and J.W. Drexler(1994) The atomic arrangement of synchysite-(Ce), CeCaF(CO3 )2 . Can. Mineral., 32, 865–871.
(3) de Parseval, P., F. Fontan, and T. Aigouy (1997) Composition chimique des minéraux deterres rares de Trimouns (Ariège, France). Compt. Rendus Acad. Sci. Paris, 324, 625–630 (inFrench with English abs.).
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