The Bastnasite Group


The Bastnasite Group minerals are not entirely structurally related and only loosely chemically related. They are however often associated, even intergrown, and have many similarities. Their structures are based on bastnasite's general structure. The structure of bastnasite is made up of stacks of carbonate ion layers and cerium fluoride layers. The CeF layers form flat hexagonal sheets with each cerium bonded to three fluorines. The carbonate layers are more complex with angled carbonate triangular groups. The other members of the Bastnasite Group must accommodate calciums layers and/or hydroxides in place of the fluorines. This can play a role in distorting or ruining the hexagonal symmetry of bastnasite into trigonal and monoclinic symmetries. However, all members of this group exhibit hexagonal or pseudohexagonal crystal habits.

The general formula for this group is X({REE}CO3(F, OH)) - Y(CaCO3) or Y(BaCO3). Where the X and Y are representing different amounts of these portions of the formula in the various members of the group. The X can be either 1, 2 or 3; while the Y can be either 0, 1, 2 or 3. The REE stands for rare earth elements, commonly cerium and lanthanum and more rarely neodymium, yttrium, lanthanum and others. The barium carbonate minerals somewhat mirror the calcium carbonate members. The following table lists the minerals of this group, their formulas and their symmetries.

Y=0

Y=1

Y=2

Y=3

X=1

Hydroxlbastnasite - (Ce, La, Y)CO3(OH, F), hexagonal

Synchysite - Ca(Ce, La, Y, Nd)(CO3)2F, monoclinic

Huanghoite - BaCe(CO3)2F, trigonal

Kukharenkoite - Ba2Ce(CO3)3F, monoclinic

Zhonghuacerite - Ba2Ce(CO3)3F, trigonal

no known minerals

X=2

no known minerals

Parisite - Ca(Ce, La)2(CO3)3F2, trigonal

Cordylite - Ba(Ce, La)2(CO3)3F2, hexagonal

no known minerals

Cebaite - Ba3Ce2(CO3)5F2, monoclinic

X=3

no known minerals

no known minerals

Rontgenite - Ca2(Ce, La)3(CO3)5F3, monoclinic

no known minerals

Popular Members of the Carbonates Class









 

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