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
Wivenhoe Gravel Pit establishing the previous course of the Thames. Two worked flints may be evidence of occupation by Homo heidelbergensis around half a million years ago. The pit, which is now water filled, is in a field off Brightlingsea Road opposite Broad Lanes. Wivenhoe Gravel Pit Wivenhoe Gravel Pit is a 2.1 hectare geological Site of Special Scientific Interest north of Wivenhoe in Essex. It is a Geological Conservation Review site. The site is the type locality for the Wivenhoe Gravel, which was laid down by the River Thames before it was diverted south to its present course by the Anglian glaciation