University of Colorado

Mineral Structure Data

Willemite Group

The blank group is composed of minerals of the general formula X2SiO4 where X is Zn (Willemite) or Be (Phenacite). X is a small divalent cation in tetrahedral coodination.

The crystal structure of willlemite.


Table 4.5.1. Willemite Group Unit Cells.


End-member        Willemite        Phenacite
Formula           Zn2SiO4        Be2SiO4

Form.Wt.          222.824          110.108
Density           4.221            2.960
Mol Volume        52.795           37.197

Z                 18               18
Cryst.Sys.        Trigonal         Trigonal

Cryst.Class       -3               -3
 
Space Group       R-3             R-3

Cell Parameters
a              13.971             12.472
c              9.334              8.252

Vol.              1577.8           1111.6

Thermal Expansion(Volumetric)
alpha         
a0  
a1 
a2 

Elastic Properties
Ks(GPa)        
G(Gpa)        

Ref.              Simonov          Zachariasen
                  (1977)           (1971)


Table 4.5.2. Willemite Group M-sites.

End-Member        Willemite        Phenacite                Willemite        Phenacite

Site M1 M1 M2 M2 C.N. 4 4 4 4 Occupant Zn Be Zn Be Point Sym. 1 1 1 1 Wyckoff Not. 18f 18f 18f 18f Frac.Coord. x .2087 .19397 .2155 .19386 y .0171 .98412 .0234 .98234 z .4156 .41547 .0815 .08454 Distances O1 1.958 1.640 O1 1.958 1.631 O2 1.952 1.645 O2 1.967 1.643 O4 1.965 1.658 O3 1.972 1.655 O4 1.957 1.637 O3 2.008 1.655 Mean 1.958 1.645 1.976 1.646 sigma .005 .009 .022 .011 Poly.Vol. 3.821 2.280 3.934 2.283 Q.E. 1.0054 1.0014 1.0048 1.0017 Ang.Var. 21.43 5.38 19.63 7.19 Site Energy -1123. -1379. -1109. -1397.

Table 4.5.3. Willemite Group Si-sites.


End-Member        Willemite        Phenacite

C.N. 4 4 Occupant Si Si Point Sym. 1 1 Wyckoff Not. 18f 18f Frac.Coord. x .2118 .19559 y .0155 .98402 z .7490 .74993 Distances O1 1.626 1.630 O2 1.611 1.628 O3 1.637 1.634 O4 1.619 1.631 Mean 1.623 1.631 sigma .011 .002 Poly.Vol. 2.191 2.222 Q.E. 1.0009 1.0009 Ang.Var. 3.29 3.81 Site Energy -4445. -4338.

Mineral Data Base Index

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