Guilherme Gualda

Mincal

Microsoft EXCEL© workbooks to calculate mineral formulae.

 

 

introduction:

Mincal is a set of Microsoft EXCEL© workbooks designed to perform the conversion of mineral compositions from weight percent of oxides into cationic abundances (see Apendix in Deer et al. 1992).

Several schemes are implemented to compute estimates of ferrous and ferric iron abundances using stoichimetric criteria, including the Method of Droop (Droop 1987), the Method of Schumacher for amphiboles (see Leake et al. 1997), as well as some variants of the latter (Gualda & Vlach 2005).

One important advantage of using these workbooks is that the user has control over the calculation procedures, allowing for customization when appropriate, which is difficult or impossible in “black box” programs developed using other programing languages.

Mincal also allows the user to take full advantage of the features already available in Microsoft EXCEL©, without the need for intermediate steps of importing and exporting files. For instance, Mincal allows the results to be easily plotted onto binary diagrams.

You can get a link to download a zip file containing all components of Mincal by filling out this form here. Or contact Guil Gualda directly by e-mail.

installation:

– Extract the contents of Mincal.zip onto a folder of your choice

– On Excel, go to Tools, Add-Ins, Browse, and search for the file Mincal.xla, and click OK

– You should see a Menu bar and a list under Tools from where you can run Mincal

use:

– Open a spreadsheet with the data you want to use, and then choose Initialize

– You will have to choose one of 5 options:

1) Simple, which means no Fe3+ estimation

2) Droop, which allows you to choose the number of cations and oxygens to do Fe3+ estimation

3) Schum_Max is the method of Schumacher, but using the maximum estimate, as we suggested in our paper

4) Schum_Avg is the method of Schumacher as originally suggested

5) Schum_Min is the method of Schumacher, but using the minimum estimate, which is unlikely to be useful except for very reducing conditions

– For Simple and Droop modes, the “Variables” sheet needs to be set:

1) for Simple mode, in the “Variables” sheet, list in column A the ions to be used, and in cell B3 the number of ions (for instance, for 6 oxygens, set A3 to O, B3 to 6; for 4 total cations, list all cations in column A, beginning in cell A3, and set B3 to 4)

2) for Droop mode, list the cations on column A, the total number of listed cations on cell B3, and the number of O in cell C3 (for example, to do 13eCNK in amphiboles, list all cations except for Ca, Na, and K in the A column, then set B3 to 13, and C3 to 23)

3, 4, 5) No “Variables” sheet, no adjustments needed

– The original data will be copied to the “Data” sheet, and the results will appear in “Result-Oxides” (except for Simple mode) and “Result-Cations” (all modes); the results are automatically updated upon changes in either “Data” or “Variables”

known issues:

– Mincal will not work with a single analysis, simply use 2 or more columns of data

– The formulas for the oxides in the input table have to be typed exactly as they appear in the “Const” sheet, or you will get the “#N/A” error (meaning it could not find the oxide of interest)

– Exercise caution when cutting, deleting, or inserting cells, as this may cause unwanted changes in the calculations; if in doubt, just restart Mincal using the data on the “Data” sheet

references:

1) Simple mode:
Deer WA, Howie RA & Zussman MA (1992) An introduction to the rock-forming minerals. Longman. 2nd Ed. London, 696 p. [ http://www.amazon.com/gp/reader/0582300940/ ]

2) Droop mode:
Droop GTR (1987) A general equation for estimating Fe3+ in ferromagnesian silicates and oxides from microprobe analysis, using stoichiometric criteria. Mineralogical Magazine 51: 431-437 [ http://dx.doi.org/10.1180/minmag.1987.051.361.10 ]

4) Method of Schumacher for amphiboles (Schum_Avg):
Leake BE & 21 members of IMA (1997) Nomenclature of amphiboles: Report of the Subcommittee on Amphiboles of the International Mineralogical Association Commission on New Minerals and Mineral Names. Mineralogical Magazine 61: 295-321 [ http://dx.doi.org/10.1180/minmag.1997.061.405.13 ]

3 & 5) Schum_Max & Schum_Min modes:
Gualda GAR & Vlach SRF (2005) Stoichiometry-based estimates of ferric iron in calcic, sodic-calcic and sodic amphiboles: A comparison of various methods. Anais da Academia Brasileira de Ciências 77: 521-534 [ http://www.scielo.br/pdf/aabc/v77n3/a12v77n3.pdf ]

 

 

 

 

 

Created by Guilherme Gualda
http://my.vanderbilt.edu/ggualda
Last update: Nov 15, 2014