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 S‹o Francisco Craton of southeastern
Brazil. It consists of quartz (gray), feldspar (white), and mafic
minerals (black).
Vizag Blue Granite (a.k.a. ÒSrikakulam Blue GraniteÓ) - 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). ÒVizag Blue GraniteÓ 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).