THIXOTROPY IN SUPRAMOLECULAR CRYSTALLIZATION AND GENESIS OF MACROSTRUCTURES OF PRECIOUS OPAL

Abstract

At the initial stage of genesis of precious opal from concentrated suspensions of monodisperse silica spheres, supramolecular gel crystals with solid silica particles form. The latter are localized at the lattice sites and are separated by liquid partings - ionic atmospheres around the particles. These crystals with weak bonds between their structural units form and exist under the balance of the forces of electrostatic repulsion of counter-ionic atmospheres, on the one hand, and the total forces of molecular attraction and gravitational compression of the particles, on the other. Under mechanical action, the balance is disturbed, and reversible thixotropic destruction (liquescency) of the structure into particles and microblocks (clusters) takes place, thus producing suspension. This suspension recrystallizes, the growth of secondary crystals being contributed by the clusters. Secondary thixotropic crystallization produces nests and veinlets in the initial structure of precious opal and accounts for a considearble diversity of macrostructural patterns of natural precious opal.