IP Israel Patents (Israel)

Colloid science has been applied by soil chemists and clay mineral ogists for many years, and some of the most important studies on the behavior of colloids have been contributed by them. Barring a fe

Rocks, rock debris, and grains are usually coated with X-ray amorphous layers formed by the following mechanisms: (1) Incongruent dissolution of rock material; (2) sorption of inorganic and organic species mainly from solutions and suspensions, but also from the atmosphere; (3) thermal diffusion of atoms from the core of the crystal to the surface resulting from abrasion and collision between solids in dry systems; (4) biologic activity, which is, however, outside the scope of this review and will not be considered.

Silica, SiO2, is common in nature and occurs as seven distinct minerals, of which five show crystalline structures (quartz, tridimite, cristobalite, coesite, and stishovite) and two are amorphous (opal-A and lechatelierite). Lechatelierite is a silica glass and is very rare. Coesite and stishovite are also very rare and are found only in meteoritic craters, where they have been formed from quartz because of the high pressure resulting from the meteoritic impact. Opal is obtained by deposition from aqueous silica solutions at low temperatures. It is deposited by thermal waters associated with igneous activity and is also secreted by sponges, radiolaria, and diatoms. The most common form of silica is quartz.