Reviewing empirical formulas

[ebesfus]

Hello everyone, and especially to the publishing team
I am calculating for each mineral its rarity index, iR. This value is described in [1] and requires knowledge of the empirical formula (EF) of each mineral. Mineralienatlas is perfect for this. Therefore, I am checking every EF to get the iR.
The issue is that I found a small error with the data from the bicapite (IMA2018-048), [KNa2Mg2 (H2O) 25] [H2PV12O40 (VO) 2]. The number of oxygen atoms is 67 and V is 14, but 66 and 13 are on your list. Consequently, other data should also be reviewed.
Please, check it and, if you agree, update that data from bicapite.
I am reviewing all minerals (EF) and if I find any other errors, I will contact you again.
Thank you and stay healthy.
[1] BES, Eduard (2021): “Método cuantitativo para determinar la rareza de los minerales basado en la abundancia de sus elementos constituyentes”. Paragénesis; vol. 3, núm. 1 (2021−1), pp. 87−102. (Quantitative method to determine the rarity of minerals based on the abundance of their constituent elements) - https://www.minercat.com/es/publicaciones/paragenesis/en-linea/2021-1

[Doc Diether]

I just looked at the Bicapite formula here in MA and I found it 67  0 and V is 14.
Best regards
Doc Diether

[guefz]

There was a small mistake in writing the formula, one number that should have been typesetted low, wasn't. Now fixed.

[Stefan]

Hello Eduard,

a rarity index sounds interesting. Is there a formula for it? We would be interested in it and could possibly output calculations automatically. If we can help each other let me know.

We have changed the mineral data accordingly:

Anthony R. Kampf; John M. Hughes; Barbara P. Nash; Joe Marty - Bicapite, KNa2Mg2(H2PV145+O42)·25H2O, a new polyoxometalate mineral with a bicapped Keggin anion from the Pickett Corral mine, Montrose County, Colorado, U.S.A. - American Mineralogist (2019) 104 (12): 1851–1856. https://doi.org/10.2138/am-2019-7027

Every hint is welcome
Thx
Stefan

[ebesfus]

Yes, actually I am working on it.
In the paper [1] I develop the methodology to calculate iR for each mineral. It requires both manual and automatic calculation. I am trying to implement it so that it can be as automatic as possible.
Now I am calculating iR for all the minerals. As an exemple, I attach a piece of excel sheet I use to calculate it.
 
[1] BES, Eduard (2021): “Método cuantitativo para determinar la rareza de los minerales basado en la abundancia de sus elementos constituyentes”. Paragénesis; vol. 3, núm. 1 (2021−1), pp. 87−102. (Quantitative method to determine the rarity of minerals based on the abundance of their constituent elements) - https://www.minercat.com/es/publicaciones/paragenesis/en-linea/2021-1

>>Sorry, but the article is in Spanish and in Catalan. Maybe I will try to translate it into English.

[etalon]

Hello Eduard,

that sounds pretty interesting. Unfortunately, I don‘t understand spanish, so I may ask a question here:

To form mineral phases it is not only necessary to have the constituting elements available. More important are the necessary geochemical environments to form that phases. How far is that taken into account by the calculations, and how is it be quantified?

Thanks,
Markus

[ebesfus]

Ok. Your question is very pertinent.
Many aspects should be taken into account when working with the concept of “rarity”.
As I explain in my article, many mineralogists have described rarity (Weiß (2018), Hazen and Ausubel (2016) among others) including factors such as formation conditions (as you point out), sporadic character, difficult access, strange composition, scarcity of deposits... (I develop all this aspects).
So, the definition of "rarity" must always be related to the bases you use to express/calculate… it.
When I define the rarity index (iR), I focus it only on the chemical composition of the mineral, that is: the elements and their abundance in the earth's crust, and the number of atoms of each element in the formula. And always working on a logarithmic basis so that very small (or high) abundance values can be smoothed out to avoid unmanageable data (iR moves from 2 to 12).
This method allows obtaining a quantitative value for rarity, not subjected to qualitative issues.
There are many more arguments in my description but this is a rapid summary of it.
I strongly emphasize the fact that this is one way to determine rarity, but that the other existing ones are also valid, of course.

BR

Weiss, Stefan (2018): Das Grosse Lapis Mineralienverzeichnis, 7a ed. Munic: Christian Weise Verlag GmbH
Hazen, R.M. and Ausubel, J.H. (2016): “On the nature and significance of rarity in mineralogy”, American Mineralo¬gist; vol. 101, pp. 1245-1251.

[ruebezahl]

Hello,

When I define the rarity index (iR), I focus it only on the chemical composition of the mineral, that is: the elements and their abundance in the earth's crust, and the number of atoms of each element in the formula. And always working on a logarithmic basis so that very small (or high) abundance values can be smoothed out to avoid unmanageable data (iR moves from 2 to 12).
This method allows obtaining a quantitative value for rarity, not subjected to qualitative issues.

Sorry, but in my opinion this constraint never can work properly. A suitable constraint of iR should also be able to predict the rarity of a potential mineral. Your concept will fail early quantifying simple issues:

Copper and Carbon both are quite common in earth's inventary, but how much native coppercarbides do you know?

Cheers
Reubezahl