quartzite

plural quartzites

1. countableuncountablechemistryA 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.

   1869, James Hall, “Notes upon the Geology of Some Portions of Minnesota, from St. Paul to the Western Part of the State”, in Transactions of the American Philosophical Society, volume XIII, page 331

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   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.

   1870 November 28, Professor Ansted, “The Passage of the Mont Cenis”, in Sylvanus Urban (pseudonym of Edward Cave), editor, The Gentleman's Magazine, volume 229, page 656

   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.

   1883, T. G. Bonney, “On a Collection of Rock Specimens from the Island of Socotra”, in Philosophical Transactions of the Royal Society, volume 174, page 273