ABSTRACT

The occurrence of rocks with the megascopic characteristics of "quartzite" does not necessarily indicate metamorphism or the proximity of crystalline basement complex. These rocks may be sedimentary. The sedimentary quartzites were originally sandstones that have subsequently undergone non-metamorphic changes ranging from cementation by secondary silica to compaction through pressure-solution of the quartz grains. By far most of the sedimentary quartzites studied are of the latter type and cannot be classified as orthoquartzites. Consequently it is proposed that the term pressolved quartzite be used instead to distinguish this ubiquitous rock. Much work remains to be done to better understand the effects of time, depth of burial, tectonic activity, and the amount and character f the interstitial fluids on the phenomenon of the transition of sandstones to pressolved quartzites.