Polymorf - Knowhwere- Fluorite

MINERALS AND SYNTHETIC COMPOUNDS, A_mX_n, WITH CLOSE

PACKED X ATOMS AND A ATOMS OCCUPYING CUBIC INTERSTICES

Fluorite

click here to see a key to this data bar
cubic	50%	cp	3-d	all edges	A- 8c, X- 4c/cp

structure

The fluorite structure is modeled here as a CP packing of X atoms with A atoms

occupying 50% of the cubic interstices of each layer. The occupied cubic voids in a

layer are interspersed with unoccupied voids in a checkerboard pattern.

Ex. CaF₂ ( calcium fluoride, fluorite ) ( Ca - A , F - X )

Crystal lattice

The fluorite crystal structure can be modeled as a simple CP lattice with the

checkerboard pattern of occupied AX₈ coordination groups of one layer colored

one color and staggered relative to the checkerboard pattern of AX₈ groups of a

different color in the layers above and below it. Unoccupied cubic voids are thus

located in the center of cubes with faces comprised of the two different colors while

the faces of each of the occupied cubic AX₈ groups are all one color or the other.

Polyhedral framework

The polyhedral framework model demonstrates the checkerboard array of AX₈

groups clearly and the edge linkage between groups.

Cleavage
(111) - perfect		twinning on (111)
		click image to enlarge
Crystal habit
cubic, octahedral, dodecahedral (rare); twinning on (111), usually cubes
.

Isostructural minerals/compounds

AuAl₂, AuGa₂, AuIn₂, AuSb₂, BaCl₂, BaF₂, CaF₂, CdF₂, CeO₂, CoSi₂, GeMg₂, HfO₂,

HgF₂, IrSn₂, NbH₂, NiSi₂, NpO₂, -PbF₂, PbMg₂, -PoO₂, PtAl₂, PtGa₂, PtIn₂, PtSn₂,

PuO₂, RaF₂, ScH₂, SiMg₂, SmH₂, SnMg₂, SrCl₂, SrF₂, ThO₂, VO₂, YH₂, ZrO₂

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Page 73 - Structure matters - Fluorite