I have a very confusing question. I understand tha Hydrolysis of granite has a formula but what is it? I get that the break down of k feldspar in granite causes the weathering of fine grains that later become clay and sand which we see on the beach, I just need an actual chemical equation for this process

I believe that granite is mostly silicon oxide, SiO2 (someone correct me if I'm wrong). It has a lot of impurities that give it its color and texture. The hydrolysis reaction is very, very slow.

SiO_2 + 2H_2O \rightleftharpoons Si(OH)_4

FYI: (Mostly 'silicite' in french, I think silica (SiO4)). Most granite rocks are made up of more than 65% of silica from a book I have and more than 10% of quartz, which is silicon oxide (SiO2).

No, it's SIO2 (silica). There are SiO4 tetrahedra making up the three-dimensional structure of both quartz and granite but the overall formula is SiO2. Silicon bonds with four bonds similarly to carbon. You don't see CO4. The SiO2 in quartz is quite pure. Granite is full of impurities. Here's the chemical composition from a Wikipedia page. It does have a lot of alumina in it also.

Granite - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Granite)

Chemical composition

A worldwide average of the average proportion of the different chemical components in granites, in descending order by weight percent, is:[2]

* SiO2 — 72.04%
* Al2O3 — 14.42%
* K2O — 4.12%
* Na2O — 3.69%
* CaO — 1.82%
* FeO — 1.68%
* Fe2O3 — 1.22%
* MgO — 0.71%
* TiO2 — 0.30%
* P2O5 — 0.12%
* MnO — 0.05%

Ok, it was only a problem of translation then, 'silice' is silica, SiO2. That means that silica and quartz have the same formula, like you said, Perito. I thought that the book was mentioning two completely different substances by mentioning silica and quartz, but it turned out that silica is just a form of SiO2 and quartz, another purer form. :o

Hello everyone,

Great topic. I am currently doing research on this subject. SiO2, SiO4 etc.

Appreciate for the info from the Subject Matter Expert point of view.

I am doing R&D and RDD in the Quarry business.


Thanks,
Zul Abdul Rahman