CHARNOCKITE
Charnockites are rather peculiar rocks - they consist of an unusual mix of
minerals, principally quartz, feldspar, and pyroxene. Charnockites can be coarsely
crystalline-textured or foliated.
Some are high-grade metamorphic rocks, while others are intrusive
igneous rocks, but all are quartzo-feldspathic with pyroxene. (more info.)
The feldspar component of charnockite
characteristically glimmers when tilted in the light (see especially the large
lower feldspar crystal in the photo of Verde Butterfly Granite below).
Ubatuba Granite from near the town of Ubatuba in southeastern
Brazil. This late Neoproterozoic to Cambrian (~650-500 million years)
charnockite has large, dark-greenish feldspars, black pyroxene, and some
quartz.
Verde Butterfly Granite - garnetiferous charnockite (a.k.a.
hypersthene monzogranite) from the Precambrian of southeastern Brazil. It
formed during the late Neoproterozoic to Cambrian (~650-500 million years
ago). The rock is dominated by feldspar (greenish), pyroxene (black),
quartz, and garnet (very deep red).
Seaweed Green Granite (a.k.a. Pocono Green Granite, Pine Green
Granite) - a garnetiferous charnockite from the Precambrian of Orissa State,
Eastern Ghats Orogenic Belt, eastern India. The very dark red garnet
component of this rock is mostly mixed with black pyroxene patches. The
black pyroxene areas are generally elongated, and aligned more or less parallel
throughout the rock (foliated texture).
Nara Brown Granite (a.k.a. Nara Granite, Caledonia Granite,
Caledonia Nara Brown Granite, Caledonia Nara Granite) - this has the appearance
of an ordinary porphyritic granite with K-feldspar phenocrysts, but petrologic
and regional geologic work shows that it is a charnockite (a porphyritic
farsundite or porphyritic quartz mangerite, to be more specific).
Geologic Unit & Age: Rivire--Pierre Plutonic Suite, Grenville Orogeny
metamorphism, late Mesoproterozoic, ~1.1 Ga.
Locality:
quarry north of town of Rivire--Pierre, Portneuf County, southern Quebec,
southeastern Canada.