Mixtures of sand, silt and less than 40% clay are called loam. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Shale, formed largely from clay, is the most common sedimentary rock. Between one-half and two-thirds of the world's population live or work in buildings made with clay, often baked into brick, as an essential part of its load-bearing structure.Ĭlay is a very common substance. Clay is used in many modern industrial processes, such as paper making, cement production, and chemical filtering. Some of the earliest pottery shards have been dated to around 14,000 BC, and clay tablets were the first known writing medium. Prehistoric humans discovered the useful properties of clay and used it for making pottery. Ĭlay is the oldest known ceramic material. Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impurities, such as a reddish or brownish colour from small amounts of iron oxide. kaolinite, Al 2 Si 2 O 5( OH) 4).Ĭlays develop plasticity when wet but can be hardened through firing. Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g.
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