University of Colorado

Mineral Structure Data

Pyroxenoid Group

The Pyroxenoid group is composed of minerals of the general formula XnSinO3n, where X is a large-radius divalent cation, typically Ca, Mn, or Fe. The symmetry is triclinic and results from a mismatch between the sizes of the divalent cation and the silicate chain. The repeat integer n, increases as the mean size of the divalent cation decreases. For wollastonite and bustamite, n = 3, for rhodonite, n = 5, for pyroxmangite and pyroxferroite, n = 7, and for ferrosilite III, n = 9. In addition to the above anhydrous proxenoids, there is also a series of hydrous pyroxenoids in which Na + H substitute for one of the divalnet cations giving us pectolite (NaHCaSi3Osub>9) and serandite (NaHMnSi3Osub>9).

The crystal structure of wollastonite.

End-Member      Wollastonite   Bustamite      Rhodonite    Pyroxmangite   Ferrosilite III
Formula         Al2SiO5      Al2SiO5      Al2SiO5     Al2SiO4(F,OH)2                    

Form.Wt. Z CrystalSystem PointGroup SpaceGroup UnitCell a(Å) b(Å) c(Å) alpha beta gamma Vol(Å3) MolarVol Density Thermal Expansion(Volumetric) alpha a0 a1 a2 Elastic Properties Ks(GPa) G(Gpa)

Mineral Data Base Index

GEOL 1010 Syllabus

GEOL 3010 Syllabus

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