Clay is a sediment composed of tiny mineral particles that are formed by the
weathering and breaking down of rocks and minerals. Clay particles are the
smallest inorganic component of soil, measuring no more than 2
µm in diameter. Clay
has a low permeability.
Clay particles are negatively charged and attract positively charged ions
(cations). These cations bind to the clay particles but can also be exchanged.
Sedimentary rock(s) - Shale