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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 ...
Gneiss with large eye-shaped feldspars. Augen (from German "eyes") are large, lenticular eye-shaped mineral grains or mineral aggregates visible in some foliated metamorphic rocks. In cross section they have the shape of an eye. [1] Feldspar, quartz, and garnet are common minerals which form augen. [2]
The streaked-augen gneiss member consists of uniform, medium-grained biotite-microcline-quartz-plagioclase gneiss, with augen that have a "stretched" or "streaked" appearance. [1] 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]
An almandine-garnet growing as a porphyroblast in a quartzitic gneiss. The garnet measures 3 cm. Location: Paraíba, Brazil. Dark-coloured porphyroblasts of garnet in mica schist at Syros, Greece. A porphyroblast is a large mineral crystal in a metamorphic rock which has grown within the finer grained matrix.
The main layers of the LHS includes non-fossiliferous, low-grade, metasedimentary rocks, metavolcanic strata and augen gneiss. These have been dated as an age ranging from 1870 Ma to 520 Ma (i.e. Proterozoic to Cambrian).
[6] At the core of the Bronson Hill belt is the Monson gneiss, rich in microcline, plagioclase, amphibole schist, and eye-shaped augen gneiss. Ultramafic oceanic crust is preserved as peridotite. Much of the terrain of central Massachusetts is formed by domes that were created in the Cambrian and Ordovician. In fact, the Ammonousuc and ...
Undulose extinction or undulatory extinction is a geological term referring to the type of extinction that occurs in certain minerals when examined in thin section under cross polarized light. As the microscope stage is rotated, individual mineral grains appear black when the polarization due to the mineral prevents any light from passing through.
The Icart Gneiss is an augen gneiss of granitic composition containing potassium feldspar. This was formed from a granite dated at using U-Pb dating on zircon grains. A foliated Perelle quartz diorite (also called Perelle Gneiss), occurs in the centre and west of the island. This is a calc-alkaline tonalitic rock.