What minerals in rocks form clays?

Certain sedimentary rocks, called claystones or shales are very rich in clay and are of commercial value. The value is dependent on the clay’s mineralogical and chemical composition and purity. Common impurities include quartz, mica, calcium carbonates, iron oxides, sulfides and feldspar.

What is the source of clay mineral?

Most clay minerals form where rocks are in contact with water, air, or steam. Examples of these situations include weathering boulders on a hillside, sediments on sea or lake bottoms, deeply buried sediments containing pore water, and rocks in contact with water heated by magma (molten rock).

What are the basic structural units of clay minerals?

Actually there are two units in the fundamental structure of clays: tetrahedron and octahedron. In each tetrahedron, Si4+ in the center is surrounded by four O2− at the corners. Then they share oxygen with each other to form a tetrahedral sheet. Similarly, a metal cation is at the center and six O2− are in the corners.

What minerals are in clay soil?

Clay minerals are composed essentially of silica, alumina or magnesia or both, and water, but iron substitutes for aluminum and magnesium in varying degrees, and appreciable quantities of potassium, sodium, and calcium are frequently present as well.

What rock makes clay soil?

Also known as residual clay. The clay particles are made by decomposing feldspars that move from where they originally formed, by water in streams, rivers, and glaciers and they pick up impurities such as other minerals and organic substances, most of the pick up iron.

Which clay mineral is most stable?

Minerals that are stable under P, T, H2O, and O2 conditions near the surface are, in order of most stable to least stable: Iron oxides, Aluminum oxides – such as hematite Fe2O3, and gibbsite Al(OH)3.

What properties make clay minerals troublesome?

Clay is a very important material in geotechnical engineering, because it is often observed in geotechnical engineering practice. Generally, this soil type has numerous problems due to its low strength, high compressibility and high level of volumetric changes.