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Improving Mindat.orgSchüllerite formula

22nd Jun 2017 02:12 UTCReiner Mielke Expert

https://www.mindat.org/search.php?name=Sch%C3%BCllerite Why is this formula different from the IMA formula https://www.mindat.org/min-40293.html?

Also https://www.mindat.org/min-43411.html why is Lileyite the Mg-analogue of Schüllerite? Isn't it the Fe analogue?

22nd Jun 2017 03:46 UTCAlfredo Petrov Manager

I don't see any difference in the formulae.

As for Lileyite, according to the formula it is Mg-dominant in one position, so schuellerite would be the Fe-dominant analogue of lileyite. But then we have the complication of whether the schuellerite formula is structurally representative or we should rather be using Sokolova's suggested end-member formula. Or does anyone even understand schuellerite's structure well enough to decide?

22nd Jun 2017 15:38 UTCPavel Kartashov Manager

If Lileyite is Mg analogue of Schuellerite (i.e. is isostructural with it), its formula must to have the same metrica A₂BCD₂Ti₂(Si₂O₇)₂(O,F)₄, because of crystallochemical positions in both minerals are the same.

So or Lileyite formula should to be Ba₂Na(Mn,Ca)(Mg,Fe³⁺,Fe²⁺)₂Ti₂(Si₂O₇)₂(O,F)₄, or Schuellerite one should to be Ba₂(Na,Fe,Ca)₃FeTi₂(Si₂O₇)₂O₂F₂.

22nd Jun 2017 15:46 UTCReiner Mielke Expert

"I don't see any difference in the formulae. " I don't anymore either, it has been changed. However this now makes no sense " The end-member formula Na2Ba2Mg2Ti2(Si2O7)2O2F2 is suggested by Sokolova et al. (2013)." And by the way just so you know I wasn't seeing things here is what was there before:

23rd Jun 2017 03:30 UTCAlfredo Petrov Manager

In that case, Reiner, it was just a cache-clearing problem. One formula had been updated and the other one hadn't, but updated automatically after clearing the cache.