universal solvent

[granpa]

Water is referred to as the “universal solvent” because it can dissolve more substances and in greater quantity than any other solvent
yet, paradoxically, 99.9% of the earth is insoluble in water.

Rocks dont dissolve in water because a rock (even a large rock) is a single immense (covalently bonded) molecule and therefore cannot dissolve.
Or, if not a single molecule, then it is a collection of long polymer-like molecules (chain silicates/Geopolymers).
This is what makes lava amorphous.

Chem 421 - Crystalline and Amorphous Polymers

Solid organic compounds consisting of ordinary small molecules tend to be crystalline, that is, the molecules pack themselves in regular three-dimensional arrays. Polymers are different; they can be amorphous (totally lacking positional order on the molecular scale) or semicrystalline (containing both crystalline and amorphous regions in the same sample).


Semicrystalline polymers have true melting temperatures at which the ordered regions break up and become disordered. In contrast, the amorphous regions soften over a relatively wide temperature range (always lower than Tm) known as the glass transition (Tg). Fully amorphous polymers do not exhibit Tm, of course, but all polymers exhibit Tg.

If they are allowed to cool slowly, these chains (chain silicates) can fold up into regular crystal structures but they are still long chains of covalently bonded atoms.
On the other hand, if it cools too quickly then the result is an amorphous glass, like obsidian



MINERALS

Silicates

Consists of a small silicon atom with a +4 charge surrounded in tetrahedral fashion by four larger oxygen atoms each having a -2 charge (Figure).
Net charge on the anion group is -4.
To satisfy this charge deficiency the SiO4 tetrahedra can either bond with cations (Fe, Mg, Ca, K, Na)
or join with other SiO4 tetrahedra through oxygen sharing.

Chain silicates (Figure) Can be either single or double chain silicates. Single chains share two basal oxygen while the double chain shares three. Two examples of this group are the pyroxenes (single chain) and amphiboles (double chain). Since the Si-O bonds are stronger than the tetrahedra-cation bonds this subgroup has fairly good cleavage in two directions.

 

[arc]

Water is referred to as the “universal solvent” because it can dissolve more substances and in greater quantity than any other solvent

yet, paradoxically, 99.9% of the earth is insoluble in water.

 

Rocks dont dissolve in water because a rock (even a large rock) is a single immense (covalently bonded) molecule and therefore cannot dissolve.

 

 

Does it not win by default? Water's superiority lies not in its strength as a solvent as much as it does in the others inferiority. It is water's ability to transform through temperature that turns it into the destructive mechanism of rock that it is. Freezing in the microscopic cracks of the hardest granites begins the processes that reduces vast mountain ranges in due time to sand and silt.

 

Continuous seasonal exposure to alternating rain, ice, snow and glaciation will "dissolve" the hardest materials. Its rather interesting that the hardest longest lasting components of rock will spend their final days before being washed out to sea as a grinding compound suspended in water cutting channels through other locations of solid rock.

[John Cuthber]

"Water is referred to as the “universal solvent”"

Not often, and only by those using rather sloppy English.

 

"Rocks dont dissolve in water because..."

Yes they do.

http://en.wikipedia.org/wiki/Weathering#Hydrolysis_on_silicates_and_carbonates

just not very well.

 

Incidentally, many rocks will dissolve in molten rock.