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Improving Mindat.orgWrong formula

27th Dec 2016 16:04 UTCReiner Mielke Expert

http://www.mindat.org/min-10986.html the formula should have Ni first not Fe.

27th Dec 2016 19:56 UTCErik Vercammen Expert

Ni put first in the formula, but shouldn't Ag not also be part of the formula?

28th Dec 2016 00:45 UTCAlfredo Petrov Manager

Not necessarily, Erik, because we don't know whether the Ag is part of the pentlandite structure itself, or whether it is present as nanoinclusions of some discreet Ag species.

28th Dec 2016 01:08 UTCPavel Kartashov Manager

Not necessarily, Alfredo.;-) Argentopentlandite exists (by the way also Fe-dominant) and it able to form solid solutions with usual pentlandite. So presence into it of argentopentladite microzones is more probable than of some other Ag-phase inclusions.

28th Dec 2016 02:00 UTCAlfredo Petrov Manager

Yes, Pavel, but you have to demonstrate that on an actual specimen of "argentian pentlandite" before you put it into the formula.


Another issue is that Mindat has the parent species formula for many chemical varieties, without including the relevant varietal element in the formula. The example here is just one of many. It may be a Mindat policy (I'm not sure) to only use parent species' formulae for varieties?

28th Dec 2016 02:46 UTCReiner Mielke Expert

" Argentopentlandite exists (by the way also Fe-dominant) " If it is iron dominant why would that be pentlandite? Why not a different species?

28th Dec 2016 10:44 UTCErik Vercammen Expert

On the page of the pentlandite group, the formula of pentlandite also lists Fe first.

28th Dec 2016 11:02 UTCŁukasz Kruszewski Expert

Reiner, Pavel meant two argentopentlandite-like species, one Fe-dominant, and one Ni-dominant.

28th Dec 2016 11:23 UTCErik Vercammen Expert

From the new IMA-list:

Argentopentlandite

Ag(Fe,Ni)8S8

A 1970-047

Russia

Zapiski Vsesoyuznogo

Mineralogicheskogo Obshchestva 106

(1977), 688

Canadian Mineralogist 12 (1973), 169

28th Dec 2016 14:38 UTCReiner Mielke Expert

Hello Erik,


Argentian pentlandite is not the same as argentopentlandite. The formula for pentlandite on the pentlandite group page needs to be changed as well. http://www.mindat.org/min-29321.html


Hello Lukasz,


I made the same mistake as Erik. :-(

28th Dec 2016 15:14 UTCErik Vercammen Expert

Reiner,

my point abotthe argentopentlandite was the fact dat iron dominates here on Ni.

28th Dec 2016 16:17 UTCReiner Mielke Expert

Hello Erik,


Yes I agree, point taken. However that is not the case with argentian pentlandite.

28th Dec 2016 21:41 UTCRalph S Bottrill 🌟 Manager

Firstly, as noted above, some chemical varieties have had their formulae revert to the IMA formulae for endmembers, which is unfortunate as its important to indicate where the chemical substitution occurs, so I have changed some.


I dont know enough about argentopentlandite but its formula implies that Ag only substitutes for one of 9 metal sites in the structure. If not then its a variety of pentlandite, but i havent done any research. This will affect how the formula of agentian pentlandite should be displayed.


Pentlandite should really be divided into two species, one Ni and one Fe dominant, regardless of whether the pure endmembers exist in nature, else the formula is misleading. This change will also affect the formulae of argentpentlandite and argentian pentlandite.
 
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