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Mineralogical ClassificationIMA Formula Changes

12th Jan 2020 17:59 UTCRonnie Van Dommelen Expert

At the end of this document are a couple dozen formula changes made by executive decision of the IMA (http://rruff.info/rruff_1.0/uploads/MM83_615.pdf).

Are there any objections if I make those changes to the "IMA Formula" items for each of those minerals?

12th Jan 2020 19:26 UTCFrank K. Mazdab Manager

Hi Ronnie, thanks for offering to make the changes.

Note that for two of the three pumpellyite-group minerals listed (poppiite and pumpellyite-(Fe3+)), the new IMA formulas are still problematic because they can't be charge-balanced with the (OH,O)2 as written (that is, including the comma... as the IMA is slowly recognizing from this "clean-up" process, end-member formulas really shouldn't have commas in them).  I would suggest you treat that group instead as ([OH]O), with no comma, indicating that to charge balance cation content of the formula, one technically needs to have one OH and one O. However, using the suggested format, maintaining the () around the pair indicates that they relate to a single formula-based site (i.e. instead just writing (OH)O would be misleading because it implies two separate sites), with the additional [ ] around the OH just for clarity.

The third pumpellyite-group mineral in the list (okhotskite), because its new end-member cation set has one less cumulative cation charge than the previous other two, will charge balance if fully hydroxylated in that site, which is what the IMA did.

12th Jan 2020 21:35 UTCRonnie Van Dommelen Expert

Frank, in that case, I should probably leave poppiite and pumpellyite-(Fe3+) as is.  I only want to change the IMA formulas, not the MinDat ones. So if the IMA is still working on fixing problems, I do not want to jump ahead.

12th Jan 2020 21:44 UTCFrank K. Mazdab Manager

Hi again Ronnie,

I'm not sure you can actually change the IMA formulas here.  I think they're periodically downloaded directly from the RRUFF website, so whatever is listed there is what we show here.  I think only the mindat or other formulas we add here are editable.  I may be wrong about this, but you'll find out as soon as you try I suppose.

14th Jan 2020 18:07 UTCŁukasz Kruszewski Expert

Indeed, the IMA formulas can't in Mindat can't be changed in the current "version". When changing the formulas to the most recent ones, I usually copy the old formula to the "formula notes", and explain if needed.

16th Jan 2020 00:44 UTCRonnie Van Dommelen Expert

Thanks guys.  I'll just leave them to be automatically updated them.

16th Jan 2020 01:09 UTCFrank K. Mazdab Manager

no worries Ronnie... we appreciate your enthusiasm and initiative.

But your post did motivate me to go in and standardize the pumpellyite-group mineral formulas (the mindat versions, not the IMA ones), so now all the species have charge-balanced end-member formulas, and the compositional relationships between them are more clear.

12th Jan 2020 20:47 UTCAlfredo Petrov Manager

We should keep the old formulae too somewhere, like in the description box?

12th Jan 2020 21:32 UTCRonnie Van Dommelen Expert

Will do.
 
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