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Augen gneiss, from the German: Augen, meaning "eyes", is a gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear-bound grains (porphyroclasts), normally feldspar, surrounded by finer grained material. The finer grained material deforms around the more resistant feldspar grains to produce this ...
The hornblende gneiss member is similar to the layered gneiss member, but with hornblende-bearing dark gneiss accounting for about half of the outcrop area. [1] The Slaughterhouse Gneiss weathers to a pinkish to orange color, and consists of relatively uniform, medium-grained microcline-quartz-plagioclase gneiss with muscovite, biotite, or both ...
Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula K(Mg,Fe) 3 AlSi 3 O 10 (F,OH) 2. It is primarily a solid-solution series between the iron - endmember annite , and the magnesium -endmember phlogopite ; more aluminous end-members include siderophyllite and eastonite .
biotite → K-feldspar + garnet + orthopyroxene + H 2 O. Hornblende granulite subfacies is a transitional coexistence region of anhydrous and hydrated ferromagnesian minerals, so the above-mentioned isograds mark the boundary with pyroxene granulite subfacies – facies with completely anhydrous mineral assemblages.
Litchfieldite (nepheline syenite gneiss) from Canaã Massif, Brazil. Litchfieldite is a rare igneous rock.It is a coarse-grained, foliated variety of nepheline syenite, [1] sometimes called nepheline syenite gneiss or gneissic nepeheline syenite. [2]
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. [1] The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram in Figure 1). [1]
A study of sodium-rich quartz-alkali feldspar—biotite gneiss granulite facies terrane in the Kerala Khondalite Belt near Manali in south India found that in situ leucosomes (light colored segregations) within the gneiss showed the development of garnet replacing the dark biotite. The study indicated localized melting or migmatization within ...
Kyanite occurs in biotite gneiss, mica schist, and hornfels, which are metamorphic rocks formed at high pressure during regional metamorphism of a protolith which is rich in aluminium (a pelitic protolith). Kyanite is also occasionally found in granite and pegmatites [9] [11] and associated quartz veins, [12] and is infrequently found in ...