University of Colorado

Mineral Structure Data

Melilite Group

The melilite group is composed of minerals of the general formula X2YZ2O7 where X is Ca or Na, Y in Al or Mg and Z is Si or Si + Al. X is a large 8-coordinated site. Y and Z are tetrahedral.

The crystal structure of melilite. 

End-Member      Na-Melilite  Gehlenite      Akermanite
Formula         CaNaAlSi2O7    Ca2Al(Al,Si)2O7     Ca2MgSi2O7


Form.Wt.        258.219       274.205       272.640
Z               2             2             2
CrystalSystem   Tetr          Tetr          Tetr
PointGroup      -42m          -42m          -42m
SpaceGroup      P-421m         P-421m         P-421m      

UnitCell
a(Å)            7.6344        7.7173        7.835
c(Å)            5.0513        5.0860        5.010

Vol(Å3)         294.41        302.91        307.55

MolarVol        88.662        91.220        92.619   
Density         2.912         3.006         2.944

Thermal Expansion(Volumetric)
alpha                         24.0        
a0                             0.2320
a1                             0.2679

Elastic Properties
Ks(GPa)        
G(Gpa)
Mineral Data Base Index

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