SYNCHYSITE

    Class : Carbonates, nitrates, borates
    Subclass : Anhydrous carbonates
    Crystal system : Monoclinic
    Chemistry : Ca(Ce,La)(CO3)2F
    Rarity : Uncommon

Synchysite-(Ce) is a calcium-cerium fluoro-carbonate, but substitution of cerium by other rare earths is common; however, it is not certain that complete solid solutions exist with the other members of the group : synchysite-(Nd) and synchysite-(Y). Synchysite occurs in a variety of geological environments. It is known in pegmatites of nepheline syenites, associated with nepheline and aegirine, and in carbonatites. Its name comes from the Greek sunchusis (confusion), because this mineral was originally confused with parisite. Synchysite forms pseudorhombohedral to thick tabular crystals, sometimes hemimorphic, of gray to gray-yellow and brown color.


Main photo : Synchysite-(Ce) from Monte Cervandone, Piedmont, Italy © Italo Campostrini

Synchysite-(Ce) from Furka base tunnel, Valais, Switzerland © Stephan Wolfsried
Synchysite-(Ce) from Rivet, Peyrebrune, Tarn, France © François Le Gaillard
Synchysite-(Ce) from Poudrette quarry, Mont St-Hilaire, Canada © Stephan Wolfsried
Synchysite-(Ce) from Trimouns, Ariège, France © Dan Weinrich

Synchysite in the World

Synchysite is known in the nepheline syenites of Narssaq (Greenland) and in the carbonatites of Mont St-Hilaire (Quebec, Canada) where it encrusts large siderite crystals. It is also reported in the Swiss alpine clefts (Piz Blas, Pizzo rotondo, Cherbadung) associated with adularia, xenotime and gadolinite. It is also described in several other sites.

Synchysite in France

In France, very beautiful crystals, almost centimetric, have been extracted from the hydrothermalized dolomites of the large talc deposit of Trimouns near Luzenac (Ariège). It is also known in millimetric crystals at La Mouline and Peyrebrune (Tarn), at Marsanges (Haute-Loire), at Valencon (Nièvre) and at Madone des Fenestres (Alpes-Maritimes).

Twinning

Twinning is known on {0001}.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 4.5
Density : 3.9
Fracture : Sub-conchoidal
Streak : White

TP : Translucent to opaque
RI : 1.674 to 1.770
Birefringence : 0.096
Optical character : Uniaxial +
Pleochroism : Low
Fluorescence : None

Solubility : Acids

Magnetism : NoneRadioactivity : None

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