Structural state and differusion of impurities in natural quartz of different genesis

Impurity inhomogeneities and other structural de- fects have been studied by means of transmission electron microscopy (TEM), X-ray microanalysis and electron para- magnetic resonance (EPR) in untreated and heat-treated quartz samples of three genetic types: hydrothermal, peg- matitic and magmatic. The impurities present are A1, Na and H20 , which occupy tetrahedral (A13+) or interstitial (Na +, H20 ) positions in the quartz lattice. Impurities form imperfections of various degrees of seg- regation: from point defects to micropores with a gas-liquid content. Their size, form, density and distribution in the lattice depend on the formation conditions of the quartz, the presence of dislocations and plane defects serving as sinks for the impurity atoms, and the heat treatment regime. Experimental data indicate that gas-liquid inclusions of di- mensions up to some microns are the result of impurity segregation during postcrystallizational cooling. Crystalline quartz amorphizes upon electron irradiation. A model of structural water explaining experimentally ob- served features of this phenomenon is proposed whereby the water molecule, represented as a dipole, enters microre- gions of the silica lattice with a high impurity content and there forms a bond between 'defective' (SiO3) 2- and (A104) 5- tetrahedra. On irradiation, the Si---O donor-ac- ceptor bonds trap nonelastically scattered electrons and are ruptured as a result. The water released by this lattice dis- continuity forms microbubbles that diffuse along sinks into the larger micropores thus further increasing their volume.