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GarnetCalc

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GarnetCalc automatically calculates garnet compositions from microprobe analyses.
Results are plotted in the P-GA-AS diagram.

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GarnetCalc – Calculation of garnet compositions

Calculation of garnet composition normalized to 8 cations with the tetrahedron position filled up with Al³⁺. Fe³⁺ estimation and end-member calculation (Uwarowite, Ti-Andradite, Andradite, Pyrope, Spessartine, Grossular, Almandine) for garnets with (Mg+Mn) < Al and (Cr+Ti+Fe³⁺) < Ca. Drawing of the P-GA-AS diagram.

You can enter the values individually in the table below or use the input fields. Here you enter for up to 5 garnets the values (oxides) as rows separated by single spaces (see placeholders; 200 characters max.). Note the order of the elements in the table: Mg, Al, Si, Ca, Ti, Cr, Mn, Fe (total Fe as FeO)! Additionally, the sample designation must come first. You can use the period or the comma as a decimal separator.
Further down below you also have the possibility to enter data for the P-GA-AS diagram manually.

Your garnets

You can also enter your data (oxides) here (into the light-blue fields).

Name
	Oxides	Oxides	Oxides	Oxides	Oxides
MgO
Al₂O₃
SiO₂
CaO
TiO₂
Cr₂O₃
MnO
FeO
Total
Settings
Ratio of Fe³⁺ to total Fe [Fe³⁺/(Fe³⁺+Fe²⁺)]

Constants and intermediate results

Garnet 1

	Oxides [wt.-%]	Mol wt. (AW)	–	Atom Prop.	Oxygen	Cations
SiO₂
TiO₂
Al₂O₃
Cr₂O₃
Fe₂O₃
MgO
CaO
MnO
FeO
Total
Fe_tot.
Garnet 2
SiO₂
TiO₂
Al₂O₃
Cr₂O₃
Fe₂O₃
MgO
CaO
MnO
FeO
Total
Fe_tot.
Garnet 3
SiO₂
TiO₂
Al₂O₃
Cr₂O₃
Fe₂O₃
MgO
CaO
MnO
FeO
Total
Fe_tot.
Garnet 4
SiO₂
TiO₂
Al₂O₃
Cr₂O₃
Fe₂O₃
MgO
CaO
MnO
FeO
Total
Fe_tot.
Garnet 5
SiO₂
TiO₂
Al₂O₃
Cr₂O₃
Fe₂O₃
MgO
CaO
MnO
FeO
Total
Fe_tot.

	Garnet 1	Garnet 2	Garnet 3	Garnet 4	Garnet 5
Fe2O3 [wt.-%]
FeO [wt.-%]
Total oxides [wt.-%]
Corr. Si cations ≤ 3
Corr. Si cations > 3
Si [wt.-%]
Ti [wt.-%]
Al [wt.-%]
Cr [wt.-%]
Fe³⁺ [wt.-%]
Mg [wt.-%]
Ca [wt.-%]
Mn [wt.-%]
Fe²⁺ [wt.-%]
Total
Fe³⁺/Fe_tot.
Mg/Mg+Fe
Fe/Fe+Mg
Z
Al³⁺ (Z)
Al³⁺ (Y)
Y
X
Difference
Total
Ca-Cr
Ca Rest
Ca-Ti
Ca Rest
Ca-Fe
Ca Rest
Mg-Al
Al Rest
Mn-Al
Al Rest
Ca-Al
Ca Rest
Al Rest
Fe-Al
Al Rest
Fe²⁺ Rest
Total
Ca-Cr (×100)
Ca-Ti (×100)
Ca-Fe (×100)
Mg-Al (×100)
Mn-Al (×100)
Ca-Al (×100)
Fe-Al (×100)
Total

Results
Garnet normalized on 8 cations, tetrahedron position filled up with Al³⁺

	Garnet 1	Garnet 2	Garnet 3	Garnet 4	Garnet 5
SiO₂
TiO₂
Al₂O₃
Cr₂O₃
Fe₂O₃
MgO
CaO
MnO
FeO
Total
Cations
Si
Ti
Al
Cr
Fe³⁺
Mg
Ca
Mn
Fe²⁺
Total
Grid occupation
Z The Z (R) site is usually occupied by quadrivalent cations in an tetrahedral framework (surrounded by four O²⁻), mostly Si⁴⁺, but also Al³⁺, Fe³⁺, Ti⁴⁺, P⁵⁺, As⁵⁺, V⁵⁺.
Al³⁺ (Z)
Y The Y (B) site is usually occupied by trivalent cations in an octahedral/tetrahedral framework, mostly Al³⁺, Fe³⁺, Cr³⁺ und V³⁺. But also Ti⁴⁺, Zr⁴⁺, Sn⁴⁺, Sb⁵⁺ or Mg²⁺, Mn²⁺. The [SiO₄]⁴⁻ is occupying the tetrahedra. On the octahedral Y site Al³⁺ can be replaced by Fe³⁺.
Al³⁺ (Y) Al³⁺ (Y): Pyralspite garnets – aluminium in Y site: Almandine (Fe₃Al₂(SiO₄)₃), Pyrope (Mg₃Al₂(SiO₄)₃), Spessartine: (Mn₃Al₂(SiO₄)₃).
X The X (A) site is usually occupied by divalent cations, mostly Mg²⁺, Fe²⁺, Mn²⁺ und Ca²⁺, but also Y³⁺ or Na⁺.
Total
Cation ratios
Fe³⁺/Fe_tot.
Mg/Mg+Fe
Fe/Fe+Mg
End-members
Uvarovite Uvarovite: Ca₃Cr₂Si₃O₁₂
Ti-Andradite Ti-Andradite: Ti-content is up to 5% in Melanites, black varieties of Andradite (Ca₃(Fe³⁺, Ti)₂Si₃O₁₂). It may even reach up to 20%.
Andradite Andradite: Ca₃(Fe³⁺, Ti)₂Si₃O₁₂
Pyrope Pyrope: Mg₃Al₂Si₃O₁₂
Spessartine Spessartine: Mn₃Al₂Si₃O₁₂
Grossular Grossular: Ca₃Al₂Si₃O₁₂
Almandine Almandine: Fe²⁺₃Al₂Si₃O₁₂
Total
P-GA-AS Diagram
P P = Pyrope
GA GA = Grossular + Andradite
AS AS = Almandine + Spessartine
Total
The ratio (FeO+MgO)/(CaO+MnO) For Ca-poor garnets there appears to be a continuous variation of (FeO+MgO) against (CaO+MnO) with metamorphic grade. The increase in (FeO+MgO)/(CaO+MnO) is a useful indicator of increase in grade (Deer et al., 19992).
FeO+MgO
CaO+MnO
(FeO+MgO)/(CaO+MnO)
P-GA-AS Diagram (normalized to 100%)
P
GA
AS
Total

Option:

Show auxiliary lines in the classification diagram

Manual input for P-GA-AS diagram

Here you may enter known values for P-GA-AS to plot them in the ternary diagram.
You need to enter a name for each garnet you want to plot in the diagram and the values must sum up to 100%.


Name
P
GA
AS

The P-GA-AS diagram

The P-GA-AS diagram The hammers

Download diagram

Captions

•	Garnet 1
•	Garnet 2
•	Garnet 3
•	Garnet 4
•	Garnet 5
Top corner	Pyrope
Right corner	Grossular + Andradite
Left corner	Almandine + Spessartine

Download data

Current date

Enter a title

Sample number, etc.

Download data file (*.csv)

Literature

Berry, A. J.; Yaxley, G. M.; Woodland, A. B.; Foran, G. J. (2010): A XANES calibration for determining the oxidation state of iron in mantle garnet. – Chemical Geology, Volume 278, Issues 1–2, 2010, Pages 31-37, ISSN 0009-2541, https://doi.org/10.1016/j.chemgeo.2010.08.019
Cottrell, E. (2023): Garnet crystallization does not drive oxidation at arcs. – Science, Vol 380, Issue 6644, pp. 506-509; https://doi.org/10.1126/science.ade3418
Deer, W.A., Howie, R.A. & Zussman, J. (1992): An introduction to the rock-forming minerals. – Longman Scientific & Technical, Harlow, 2nd edition 1992: 696 p.
Kiseeva, E.S., Vasiukov, D.M., Wood, B.J. et al. (2018): Oxidized iron in garnets from the mantle transition zone. Nature Geosci 11, 144–147 (2018). https://doi.org/10.1038/s41561-017-0055-7
Matthes S. (1987): Mineralogie – Eine Einführung in die spezielle Mineralogie, Petrologie und Lagerstättenkunde. – Springer-Verlag, Berlin, Heidelberg, 1987: 444 p.

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