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One of the interesting aspects of #Bornite is how it defies the simplistic model of ionic bonding and charge. For example, if I give you a plag: CaAl₂Si₂O₈, few would struggle to see that calcium is divalent, aluminium trivalent, and silicon tetravalent. Bornite? Let's see.
Bornite is Cu₅FeS₄ (ideally, let's not get into the Pandora's box which is non-stoichiometric bornite).
So what's with the sulfur? Is it monovalent like pyrite (FeS₂) or divalent like pyrrhotite (~FeS)? Each selection requires different allocation of Cu¹⁺ and Cu²⁺,...
So what's with the sulfur? Is it monovalent like pyrite (FeS₂) or divalent like pyrrhotite (~FeS)? Each selection requires different allocation of Cu¹⁺ and Cu²⁺,...
...and don't work well. A paper tried to answer the question:
https://doi.org/10.1016/j.gca.2006.02.007
Siew Wei Goh et al 2006 GCA:
"The oxidation states of copper and iron in mineral sulfides, and the oxides formed on initial exposure of chalcopyrite and bornite to air". Let's see what they say.
https://doi.org/10.1016/j.gca.2006.02.007
Siew Wei Goh et al 2006 GCA:
"The oxidation states of copper and iron in mineral sulfides, and the oxides formed on initial exposure of chalcopyrite and bornite to air". Let's see what they say.
This.
Some indication of Fe³⁺!
Some indication of Fe³⁺!
It's probably all Cu¹⁺
So it should be "formally" Fe³⁺, although not quite.
So there is no answer...
The thing is, the ionic model works well for things on the far end of the periodic table. NaCl? Great.
Once things don't have a huge difference in electronegativity, the bonding is much more covalent and there isn't a complete charge transfer.
Once things don't have a huge difference in electronegativity, the bonding is much more covalent and there isn't a complete charge transfer.
Sulfides also have some metallic bonding character to them, which is why they look metallic (sort of).
Attempting to describe them with "formal charges" is looking for something that does not necessarily exist.
And that's why you need to vote for #bornite.
@MineralCup
Attempting to describe them with "formal charges" is looking for something that does not necessarily exist.
And that's why you need to vote for #bornite.
@MineralCup
