Quartz-rock

Quartz-rock, or QUARTZITE, is a commonly occurring rock, composed of an aggregate of quartz-grains welded together. It is usually white, gray, or rusty yellow or reddish in colour, and has a splintery fracture. Under the microscope the grains show a rounded and often semi-fused appearance, as if they had been mutually agglutinated while in a softened condition. The siliceous paste in which the granules are frequently set has usually a crystalline texture, and now and again crystals of quartz are developed in it. The rock not infrequently shows false-bedding, and occurs in strata of variable thickness, often forming mountain-masses. Sometimes it assumes a foliated structure (Quartz-schist), and contains scales of mica which occasionally form layers or laminae. The rock is obviously of sedimentary origin, and has subsequently been subjected to metamorphic action.