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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 gneiss is locally mylonitic with a strong gneissic metamorphic fabric defined by alignment of micas. A typical modal composition is 35% quartz, 30% plagioclase, and 20% potassium feldspar, 7% muscovite, 6% biotite, 1% opaques, and 1% trace minerals.
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 ...
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock.
Tonalite is an igneous, plutonic rock, of felsic composition, with phaneritic (coarse-grained) texture. Feldspar is present as plagioclase (typically oligoclase or andesine ) with alkali feldspar making up less than 10% of the total feldspar content.
The Meeberrie Gneiss is a generally ductilely deformed banded gneiss of monzogranitic composition, and its protolith is interpreted as a set of monzogranite sills or lopolithic intrusions. The gneiss is heavily banded by layers of amphibolite-K-feldspar-quartz of varying grainsize, plus networks of pegmatite veins.
The oldest Peninsular Gneiss found in areas in the Hosur – Gorur – Holenarsipur – Hunsur belt 3.3–3.2 Ga. The second generation Peninsular Gneiss found in the Bengaluru– Chickmagalur –Holenarsipur region 3.0–2.9 Ga a) Grandiorite facies in the Bengaluru Gneisses established by the Single Zircon Kober evaporation 207 Pb/ 206 Pb data.
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]