quartzite

1. (mineralogy) A metamorphic rock from sandstone, consisting of interlocking grains of quartz.Examples: "Following the course of the river from New Ulm to Fort Ridgely, there are several exposures of reddish-brown “granite” or quartzites, which has been quarried in a few places, but I do not feel entirely sure of its connection with the rocks in the prairie or at the Ferry below."; "The stone experimented upon being of the hardest and toughest kind the effect is not seen for several strokes ; but within two minutes, during which the writer watched the experiment, a steel chisel was completely blunted and rendered useless, and there was a hole made about two inches deep in the mass of quartzite placed to operate upon."; "Granites of the usual type, compact reddish or greyish quartz-felsite or rhyolite alternate one with another. A mica-trap is also found. Evidently this is an extension of the last group of rocks. A specimen of epidotic quartzite proves that there are, at any rate, some indications of the metamorphic series."countableuncountable