Members of the astrophyllite group are chain silicates that do not belong to either the pyroxene or the amphibole group. They have the general formula
- A :
-
= K, Na,Cs
- B :
-
= Fe,Mn
- C :
-
= Ti,Nb,Zr
Members of the group are as follows:
Astrophyllite: (K,Na)3(Fe,Mn)7Ti2Si8O24(O,OH)7
Cesium-kupletskite: (Cs,K,Na)3(Mn,Fe)7(Ti,Nb)2Si8O24(O,OH,F)7
Kupletskite: (K,Na)3(Mn,Fe)7(Ti,Nb)2Si8O24(O,OH)7
Niobophyllite: (K,Na)3(Fe,Mn)6(Nb,Ti)2Si8(O,OH,F)31
Zircophyllite: (K,Na,Ca)3(Mn,Fe)7(Zr,Nb)2Si8O27(O,OH,F)4
A solid-solution series exists between astrophyllite (Fe>Mn) and kupletskite (Mn>Fe) and between kupletskite and cesium-kupletskite (Cs>K,Na). Niobophyllite has Nb>Ti and zircophyllite has Zr>Ti in the octahedral sites.
The structure consists of chains of silica tetrahedra cross-linked into sheets by C-ion octahedra, giving these minerals perfect basal {001} cleavage. Unlike the micas,the cleavage flakes are brittle. Triclinic crystals are tabular. Occurrence is rare; the minerals...
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Reference
Phillips, W. R., and Griffen, D. T., 1981. Optical Mineralogy, The Nonopaque Minerals. San Francisco: Freeman, p. 530.
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© 1981 Hutchinson Ross Publishing Company
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Frye, K. (1981). Astrophyllite group . In: Mineralogy. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30720-6_12
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DOI: https://doi.org/10.1007/0-387-30720-6_12
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