QUARTZITE
(METAQUARZITE)
Quartzite is a common, crystalline-textured,
intermediate- to high-grade metamorphic rock. It forms by metamorphism of quartzose
sandstones or siltstones. Quartzite
can be entirely composed of interlocking quartz crystals, or the original sand
grains may still be visible. This
rock is hard (H = 7), will not bubble in acid (unlike marble), and can be
almost any color (see photos of 4 color variants below).
The term “quartzite” has been used in
geology to refer to crystalline, quartzose metamorphic rocks and to
hard, well-cemented quartzose sandstones that have not been subjected to
metamorphism. It is difficult to not call hard, well-cemented
sandstones “quartzite” (for example, the Clinch Quartzite in the
Appalachian Mountains & the Eureka Quartzite of the Great Basin in western
USA). But the Clinch and Eureka aren’t metamorphic rocks. The
term metaquartzite has been used by some geologists to refer to
crystalline-textured, quartzose rocks that have been metamorphosed (see samples
below). This implies that “quartzite”
be restricted to well-cemented, non-metamorphosed sandstones. I don’t
often see the term metaquartzite used in the geologic literature.
Quartzite (metaquartzite), 3.1 cm across.
Quartzite (metaquartzite), 3.9 cm across.
Quartzite (metaquartzite), 2.6 cm across.
Quarzite
(metaquartzite), 3.0 cm across.