Kinawa Granite - an Archean-aged migmatite from Brazil. It formed about 2.72-2.75 billion years ago by metamorphism of an older precursor rock (protolith) that dates to about 3.00-3.38 billion years. This migmatite is quarried in the southern São Francisco Craton of southeastern Brazil. It consists of quartz (gray), feldspar (white), and mafic minerals (black).
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Migmatites are very high grade metamorphic rocks that form by partial melting of gneisses. The felsic minerals have melted, cooled, and recrystallized - they form the light-colored, crystalline-textured bands in the rock. The mafic minerals have higher melting temperatures and still retain their metamorphic foliated character.
Tags: kinawa granite migmatite Precambrian sao francisco craton brazil
Vizag Blue Granite (a.k.a. “Srikakulam Blue Granite”) - a garnetiferous migmatite (also identified as a charnockitized gneiss) from India. This is one of my favorite decorative stones. It has a significant purplish-gray quartz component and is speckled with abundant reddish garnets. This rock is quarried in the Tekkali area, Palasa, Srikakulam District, far-northeastern Andhra Pradesh State, southeastern India. It is named after the nearby city of Visakhapatnam. The three dominant colors represent quartz (purplish gray), garnet (red), and hypersthene pyroxene (black wavy foliations). “Vizag Blue Granite” is a Precambrian migmatite from the northern parts of India's Eastern Ghats Orogenic Belt. It formed by Proterozoic metamorphism of a late Archean to early Proterozoic precursor rock (protolith).
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Migmatites are very high grade metamorphic rocks that form by partial melting of gneisses. The felsic minerals have melted, cooled, and recrystallized - they form the light-colored, crystalline-textured bands in the rock. The mafic minerals have higher melting temperatures and still retain their metamorphic foliated character.
Tags: vizag blue granite migmatite Andhra Pradesh India Precambrian Eastern Ghats garnet
Migmatite (8.1 centimeters across at its widest)
Metamorphic rocks result from intense alteration of any previously existing rocks by heat and/or pressure and/or chemical change. This can happen as a result of regional metamorphism (large-scale tectonic events, such as continental collision or subduction), burial metamorphism (super-deep burial), contact metamorphism (by the heat & chemicals from nearby magma or lava), hydrothermal metamorphism (by superheated groundwater), shear metamorphism (in or near a fault zone), or shock metamorphism (by an impact event). Other categories include thermal metamorphism, kinetic metamorphism, and nuclear metamorphism. Many metamorphic rocks have a foliated texture, but some are crystalline or glassy.
Migmatite is the result of very high-grade metamorphism and the partial melting of gneiss. Migmatite is a half-metamorphic, half-igneous rock with a half-gneiss, half-granite appearance. It has both foliated and crystalline textures. The granite portions of migmatite (see the pinkish/orangish/salmon-colored bands in the above specimen) formed from cooling of partially melted gneiss.
Tags: migmatite metamorphic rock rocks metamorphism foliation foliated partial melting
"Juparana Colombo Granite" - Precambrian migmatite from India.
Migmatites are very high grade metamorphic rocks that form by partial melting of gneisses. The felsic minerals have melted, cooled, and recrystallized - they form the light-colored, crystalline-textured bands in the rock. The mafic minerals have higher melting temperatures and still retain their metamorphic foliated character.
Locality: apparently derived from a quarry at the town of Thogaimalai, central Tamil Nadu State, Northern Madurai Block, Pandyan Mobile Belt, Southern Granulite Terrain, southern India
Tags: Juparana Colombo Granite migmatite decorative stone stones India Tamil Nadu Southern Granulite Terrain Northern Madurai Block Pandyan Mobile Belt
"Juparana Colombo Granite" - Precambrian migmatite from India.
Migmatites are very high grade metamorphic rocks that form by partial melting of gneisses. The felsic minerals have melted, cooled, and recrystallized - they form the light-colored, crystalline-textured bands in the rock. The mafic minerals have higher melting temperatures and still retain their metamorphic foliated character.
Locality: apparently derived from a quarry at the town of Thogaimalai, central Tamil Nadu State, Northern Madurai Block, Pandyan Mobile Belt, Southern Granulite Terrain, southern India
Tags: Juparana Colombo Granite migmatite decorative stone stones India Tamil Nadu Southern Granulite Terrain Northern Madurai Block Pandyan Mobile Belt