Petrology Homework Exercise

 

Given the following mineral compositions (Fe is Fe+2 unless indicated):

 

Staurolite (St)               (Fe,Mg)2Al9O6[(Si3Al)O16](OH)2

Chloritoid (Ctd)            (Fe,Mg)2Al4O2[Si2O8](OH)4

Anorthite (An)              CaAl2Si2O8

Glaucophane (Gln)        Na2Mg3Al2[Si8O22](OH)2

Vesuvianite (Ves)         Ca10(Fe,Mg)2Al4[Si2O7]2[SiO4]5(OH)4

Calcite (Cal)                 CaCO3

Epidote (Ep)                 Ca2Fe+3Al2O[Si2O7][SiO4](OH)

Kyanite (Ky)                Al2SiO5

Biotite* (Bt)                 KFeMg2[AlSi3O10](OH)2

Garnet* (Grt)               Fe2.1Mg0.9Al2[Si3O12]

Muscovite (Ms)            KAl2[AlSi3O10](OH)2

Cordierite (Crd)           (Fe,Mg)2Al4Si5O18 .H2O

Diopside (Di)                Ca(Fe,Mg)Si2O6

Grossular (Grs) Ca3Al2Si3O12

Andalusite (And)          Al2SiO5

Hypersthene (Hy)         (Fe,Mg)SiO3

Wollastonite (Wo)        CaSiO3

 

* I picked an intermediate composition rather than one of the end-members.

Show your calculations for all of the following:

points

(4)     1) Calculate and plot St, Ctd, Ves, Cal, An, Glc, and Ep on an ACF diagram.

 

(2)     2) Calculate and plot Ky, Bi, Grt, and Ms on an AKF diagram.

 

(2)     3) Calculate and plot Bt and Grt on an AFM diagram (projected from Mu).

 

(8)     4) You are studying a suite of rocks from a field area.  You notice that the rocks contain the following mineral assemblages:

 

And-An-Crd                An-Di-Grs                    Grs-Di-Wo

 

An-Crd-Hy                  An-Hy-Di                    

 

Calculate and plot these assemblages on an ACF diagram (plot the minerals, and connect coexisting phases with tie-lines).  What metamorphic facies is represented (see chapter 25)?  Why do some rocks have cordierite and others diopside?

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