Soil mechanics weathering of feldspar, which is the most common mineral present in igneous rock. The most common mineral constituent of silt and sand is quartz, also called silica, which has the chemical name silicon dioxide. The reason that feldspar is most common in rocks but silica is more prevalent in soils is that feldspar is much more soluble than silica. Silt, Sand, and Gravel are basically little pieces of broken rocks. According to the Unified Soil Classification System, silt particle sizes are in the range of 0.002 mm to 0.075 mm and sand particles have sizes in the range of 0.075
Soil mechanics may be given the classification symbol "GW" (well-graded gravel), "GP" (poorly graded gravel), "GM" (gravel with a large amount of silt), or "GC" (gravel with a large amount of clay). Likewise sands may be classified as being "SW", "SP", "SM" or "SC". Sands and gravels with a small but non-negligible amount of fines (5–12%) may be given a dual classification such as "SW-SC". Clays and Silts, often called 'fine-grained soils', are classified according to their Atterberg limits; the most commonly used Atterberg limits are the Liquid Limit (denoted by "LL" or formula_39), Plastic Limit (denoted by "PL" or formula_40), and