metaquartzite

(from the article `quartzite`) ...of silica from interstitial waters below the Earth`s surface; these rocks are called quartz arenites, whereas those produced by recrystallization ...
Found on http://www.britannica.com/eb/a-z/m/79

Metaquartzite

Metaquartzite is a metamorphosed sandstone, in which the grains of silica have fused together to form a hard, massive rock. Metaquartzite contains more than 90 percent quartz, which gives the rock a pale, sugary appearance. Metaquartzite is a fine to medium-grained rock formed at great heat under relatively low pressure.
Found on http://www.probertencyclopaedia.com/browse/HM.HTM
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