a metamorphic rock consisting mainly of quartz, as well as sericite, alunite, pyrophyllite, kaolinite, andalusite, and diaspore.
Typical accessory and admixture minerals are represented by corundum, topaz, rutile, and hematite embedded in the quartz grains or compressed between them. Deposits of secondary quartzites form as a result of the hydrothermal-metasomatic transformations of acidic and intermediate effusive rocks and their tuffs and, more rarely, of acidic intrusive rocks. In terms of the mode of occurence, the deposits of secondary quartzites are solid masses measuring up to several kilometers in cross section. Mineral deposits (including alunite and pyrophyllite) as well as gold-ore, copper-molybdenum, polymetallic, and copperpyrite deposits are associated with secondary quartzites. In the USSR secondary quartzites are found in Central Kazakhstan, Transcaucasia, and the Altai.