CHEMICAL FACTORS INFLUENCING THE RATES AND SEQUENCES OF SILICA PHASE-TRANSITIONS - EFFECTS OF ORGANIC-CONSTITUENTS

Dissolved organic matter affects the solution chemistry, hence silica recrystallization reactions, in laboratory experiments. In the presence of organic matter, the reaction rates of silica phase transitions (opal-A to opal-CT) are reduced, and the opal-CT phase produced is more "ordered" (lower d(101) spacing) than that in the absence of organic materials. The degree of this decrease in d(101) spacing depends on the solution properties of the organic materials used in the experiments. The lower the pH of a solution and the higher its organic alkalinity, the slower the formation rate of opal-CT and the lower the d(101) spacing of the opal-CT phase that forms. © 1990.