quartzite

noun

1. (countable, uncountable)A metamorphic rock from sandstone, consisting of interlocking grains of quartz.

   “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.”