MIGMATITE

 

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.

 


 

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 Sčo Francisco Craton of southeastern Brazil.  It consists of quartz (gray), feldspar (white), and mafic minerals (black).

 


 

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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