Horst,
Pistacite is not a mineral name but a molecule, and it is defined
as having 3Fe pfu. Holland and Powell confused the issue by calling
Ps33 pistacite. Epidote should be defined as Ca2FeAl2Si3O12(OH)
where the boundary with Cz would be at Ps16.7. The problem is that
some rapidly grown epidotes have cation disorder.
eric
>Hi Folks,
>
>I have a problem with the nomenclature of the Epidote group minerals.
>
>The principle formular can be written as Ca2(Fe3+,Al)Al2(Si2O7)(SiO4)OOH.
>There is an Fe-Endmember, called "Pistacite", containing 1 Fe3+ pfu
>(Ps100). There also is a monoclinic Fe-free endmember (Ps00), which is
>called "Clinozoisite". So far so good, but what is "Epidote"?
>Some papers distinguish between clinozoisite and epidote at a Ps-content of
>50, to be consistent with other nomenclatures. Some papers put the line to
>Ps33, because optical character changes from positive to negative at that
>point. Some even call the entire series from Ps00 to Ps100 "clinozoisite".
>Is there an official nomenclature of the epidote group minerals?
>
>Thanx, horst
>
>- -
>=================================
>Horst Marschall
>Mineralogisches Institut
>Universitaet Heidelberg
>INF 236
>69120 Heidelberg
>++49-(0)6221-546021
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