Climate, and the prevailing weather, is the main factor that cause the break up of rock ("weathering") that eventually transforms rock into soil. This happens either by physical means, when rock is broken down due to the effects of thermal or mechanical means, or by chemical means, when rock reacts with the elements round it.

Hydrolysis

This occurs when water molecules (H2O) separate into 2 charged particles, H+ (a Hydrogen ion) and OH- (a Hydroxyl ion). These ions attack the bonds that hold minerals together. Hydrolysis not only causes rock disintegration but it also changes the chemical nature of the minerals:-

Carbonation

This is an accelerated form of hydrolysis, which is caused by biological activity within the soil. The majority of soil organisms respire carbon dioxide (CO2). When CO2 comes into contact with water, a proportion of it dissolves to form carbonic acid (rain is naturally acidic for this reason). Plant roots are particularly destructive, because in addition to the carbonic acid produced, they also secrete sugars which are converted to acids by micro-organisms.

Hydration

During hydration minerals absorb water and the water molecule remains intact. Clay soils absorb water.
 

Dissolution

Minerals dissolve in water, and these are then washed away in solution.
 

Oxidation and reduction

Oxidation is a mineral's tendency to take up oxygen (O2), whilst reduction is its ability to lose oxygen.