File:Garnet-biotite rock, Beartooth Mountains MT.jpg

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Garnet-biotite rock (3.8 cm across at its widest) from the Precambrian of Montana, USA.

This gorgeous rock is dominated by deep red, rounded garnet crystals and lustrous black biotite mica. It is from an alteration halo around Archean-aged, magnetite-rich meta-iron formation. It, and the enclosed meta-iron formation, formed during two metamorphic episodes in the Precambrian: one in the Paleoarchean, at about 3.4 Ga (granulite-facies metamorphism) and another at about 2.8 Ga (upper amphibolite facies metamorphism).

Locality: Quad Creek section (= locality of Mueller et al., 1987, Geological Society of America Centennial Field Guide, Rocky Mountain Section, pp. 75-76) - roadcut on southern side of Beartooth Highway (Rt. 212), immediately west of Quad Creek, between milepost 50 and milepost 51, southern side of Rock Creek Canyon, just north of the eroded edge of Beartooth Plateau, southwest of the town of Red Lodge, Beartooth Mountains, southern Montana, USA (45° 01' 41.27" North & 109° 24' 55.31" West).

Source Garnet-biotite rock (alteration halo around magnetite-rich meta-iron formation) (Archean, metamorphism at about 3.4 Ga & about 2.8 Ga; Quad Creek section - roadcut along the Beartooth Highway, Beartooth Mountains, southern Montana, USA)
Author James St. John


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current23:53, 13 September 2014Thumbnail for version as of 23:53, 13 September 20142,188 × 2,192 (2.71 MB)Tillman (talk | contribs)Transferred from Flickr via Flickr2commons
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