Laterites and gossans can also form a concentration of resistant minerals, such as free-milling gold, by the downward leaching of soluble minerals within the matrix. Soils form by the slow weathering of solid rock. In dry mountainous regions, the soil zones may be poorly developed with only a few inches of topsoil directly above bedrock.
Climates affect the type of soils formed.
As an example, granite weathers to quartz and feldspar. In turn, quartz weathers to sand, and feldspar weathers to clay. The B -zone consists of roots, more clay, and iron oxides. The lowest C -zone consists of partly weathered rock resting above the bedrock. The effect of physical weathering is best seen in hilly or mountainous areas where freezing and thawing, forest fires, cloud bursts, tree roots, gravity and other mechanical agents break rocks apart to form smaller pieces.