Primary clay - Ichijinendo

…However, there are also uses that take advantage of the porosity, and in some cases the material is roughened to increase the porosity. The main material for pottery is secondary clay, which is formed by the accumulation of soil particles carried by water or wind. There are few examples of the use of primary clay, which is formed by the weathering of bedrock, mainly composed of siliceous rock, into soil in situ. In general, secondary clay has stronger plasticity and viscosity than primary clay. …

*Some of the terminology that refers to "primary clay" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…しかし他方では，多孔質を生かす用途もあり，むしろ多孔質を増すように粗く仕上げることも行われている。土器の材料は，水や風に運ばれた土の粒子が堆積した二次粘土を主とし，ケイ(珪)石を主体とする母岩が風化してその場で土と化した一次粘土の使用例は少ない。一般に一次粘土より二次粘土の方が，可塑性も粘性も強い。…

※「一次粘土」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報