File:"Dakota Mahogany Granite" (porphyritic granite, Milbank Granite, 2.6-2.7 Ga, Neoarchean; east of Milbank, South Dakota, USA) (14618866119).jpg

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"Dakota Mahogany Granite" - porphyritic granite from the Precambrian of South Dakota, USA.

"Granite" in the decorative stone trade is any relatively hard rock that will take a fine polish, regardless of mineralogy or chemistry or geologic origin.

"Granites" turn out to be felsic to mafic intrusive igneous rocks (granite, granodiorite, porphyritic granite, rapakivi granite, orbicular granite, pegmatitic granite, graphic granite, anorthosite, monzonite, gabbro, norite, gabbronorite, dolerite, diabase, charnockite, etc.) and high-grade to very high-grade metamorphic rocks (metanorthosite, gneiss, metaconglomerate, amphibolite, quartzite, granulite, migmatite).

True granites (= monzogranites & syenogranites & porphyritic varieties) make up most of the commercial granite trade. Countless varieties are quarried around the world.

Dakota Mahogany Granite is a porphyritic granite from the Milbank Granite (late Neoarchean, 2.6-2.7 billion years). It is quarried just east of Milbank, in northeastern Grant County, northeastern South Dakota, USA. The large brownish-salmon colored crystals are potassium feldspar (K-feldspar) (KAlSi3O8 - potassium aluminosilicate). The bluish-gray, glassy-looking crystals are quartz (SiO2 - silica). The black crystals are ferromagnesian mineral(s).
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Source "Dakota Mahogany Granite" (porphyritic granite, Milbank Granite, 2.6-2.7 Ga, Neoarchean; east of Milbank, South Dakota, USA)
Author James St. John

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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/14618866119 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

5 December 2019

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current05:44, 5 December 2019Thumbnail for version as of 05:44, 5 December 2019989 × 967 (2.44 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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