Experimental Investigation of Effects of Coatings on Quartz Growth: ABSTRACT

Abstract

Observations made on sandstones indicate that in many places coatings on quartz grains may have inhibited the development of secondary quartz. Experimental data substantiate these observations in that thin synthetic coatings of muscovite, chlorite, kaolinite, and illite inhibit the development of synthetic secondary quartz. Basal plates of quartz were coated with these materials and placed in the growth zone of hydrothermal reactors at temperatures ranging from 300°C. to 330°C. and pressures from 6,000 psi. to 10,000 psi. Solutions of 0.03M K2CO3 were used as the solvent. The precise effects of calcium carbonate and iron oxide coatings could not be determined because these materials altered to calcium silicate and iron silicate. However, thin coatings of these silicates were effective in restricting the formation of secondary quartz. Quartz grains naturally coated with clay minerals and iron oxide also showed practically no growth; whereas clean sands became highly cemented under the same experimental growth conditions. If the various mechanisms for the formation of coatings are understood and environmental conditions of deposition are known, then it may be possible to predict the location of zones in which considerable porosity would be preserved by grain coatings which restricted the development of secondary quartz. End_of_Article - Last_Page 457------------