[Atomic-S (OP)]

Is there any energy-efficient way to replace silicon by carbon in feldspar on an industrial scale?

[Chemistry4me]

Is there any energy-efficient way to replace silicon by carbon in feldspar on an industrial scale?

[Ophiolite]

I can't think of any carbon based compound that is analagous to any of the feldspars, either the plagioclases, orthoclases, or any of the rare ones. I echo Chemistry4me's question - what makes you think this is even possible?

[lightarrow]

Is there any energy-efficient way to replace silicon by carbon in feldspar on an industrial scale?

Without destroying the solid's structure is impossible.

[Bored chemist]

If you leave the rocks outside for a long time, weathering will convert some of the components to carbonates.

[Atomic-S (OP)]

I can't think of any carbon based compound that is analagous to any of the feldspars, either the plagioclases, orthoclases, or any of the rare ones. I echo Chemistry4me's question - what makes you think this is even possible?

I don't know that it is. That is why I am asking.

[lightarrow]

If you leave the rocks outside for a long time, weathering will convert some of the components to carbonates.

You forgot to say how much 'for a long time'... []

[Ophiolite]

I can't think of any carbon based compound that is analagous to any of the feldspars, either the plagioclases, orthoclases, or any of the rare ones. I echo Chemistry4me's question - what makes you think this is even possible?

I don't know that it is. That is why I am asking.

You may feel this is nitpicking, but that is not what you were asking. You asked if it were possible to do this in 1) an energy efficient way, 2)on an industrial scale. Asking those two very specific questions strongly implied that you thought the reaction itself was wholly possible.

[Bored chemist]

It's perfectly possible, as I said. It just takes a while (Asks amy passing geologists; is this millions of years or what?) and, of course, you don't get an exact exchange of carbon for silicon because carbonates just don't form the same structures as silicates.

[Ophiolite]

and, of course, you don't get an exact exchange of carbon for silicon because carbonates just don't form the same structures as silicates.

I read into the op that he is looking for a structural replacement of specific atoms in the mineral, not a wholesale replacement of one mineral by another.
I'm racking my brain and can't think of an example of feldspars being replaced by carbonates. Since you say it is perfectly possible could you give me an instance?

[Bored chemist]

This sort of thing (OK, only part of the silica is replaced by CO2 (as K2CO3)).
http://www.classzone.com/books/earth_science/terc/content/visualizations/es1202/es1202page01.cfm?chapter_no=visualization

[Ophiolite]

This sort of thing (OK, only part of the silica is replaced by CO2 (as K2CO3)).

Sorry, but I can't accept that. There is no replacement at all. The feldspar has the potassium leached from it. A typical reaction might be this.

4 KAlSi3O8 +4H⁺ + 2H20 = Al4Si4O10(OH)8 + 8Si02

The tectosilicate feldspar has been weathered to a phyllosilicate clay. The leached potassium could certainly link up with carbonate ions, but it would be wholly wrong to say the carbon had replaced the silicon.

[Bored chemist]

Where does the H+ come from?
The only practical source in rain water is CO2 acting as an acid.

That equation isn't balanced, I think this one's better.

2 CO2 + 2 H2O + 4 KAlSi3O9  --> Al4Si4O10(OH)8 +8SiO2 + 2 K2CO3
The potassium which was present as a mixed silicate is washed away as carbonate.

Incidentally, since there isn't a stable carbonate of aluminium this project is doomed from the start for any rock with Al in it. I think we should all give up on it.