| definition |
- A loose, earthy, extremely fine-grained, natural sediment or soft rock composed primarily of clay-size or colloidal particles and characterized by high plasticity and by a considerable content of clay mineral and subordinate amounts of finely divided quartz, decomposed feldspar, carbonates, ferruginous matter, and other impurities; it forms a plastic, moldable mass when finely ground and mixed with water, retains its shape on drying, and becomes firm, rocklike and permanently hard on heating or firing.
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| Abstract from DBPedia | Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2Si2O5(OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay particles, but become hard, brittle and non–plastic upon drying or firing. 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. Clay is the oldest known ceramic material. Prehistoric humans discovered the useful properties of clay and used it for making pottery. Some of the earliest pottery shards have been dated to around 14,000 BC, and clay tablets were the first known writing medium. Clay is used in many modern industrial processes, such as paper making, cement production, and chemical filtering. 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. Clay is a very common substance. Shale, formed largely from clay, is the most common sedimentary rock. Although many naturally occurring deposits include both silts and clay, clays are distinguished from other fine-grained soils by differences in size and mineralogy. Silts, which are fine-grained soils that do not include clay minerals, tend to have larger particle sizes than clays. Mixtures of sand, silt and less than 40% clay are called loam. Soils high in swelling clays (expansive clay), which are clay minerals that readily expand in volume when they absorb water, are a major challenge in civil engineering.粘土（ねんど、英: clay）は、以下のような意味をもつ言葉。 1.
* 原義は、地層中などから得られ、焼き物（陶磁器や土器）の素材にもなる「粘っこい土」のこと。「ねばつち」「へなつち」とも読む。 2.
* 学術・産業上は「非常に細かい粒子でできた堆積物」として定義される。 3.
* 土粘土のほか塑造やモデリング用に商品化された粘土様の造形材料のこと。学校教材としても馴染みが深い。 以下、上記 2. を「堆積物としての粘土」、3. を「造形材料としての粘土」とし、それぞれについて解説する。 (Source: http://dbpedia.org/resource/Clay) |
