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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]
Gneiss (/ n aɪ s / nice) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F).
Gneiss is connected to the lower part of the massif and includes minerals such as muscovite, biotite and augen. Mica schist tends to occur in thin bands while gabbro amphibolites represent the metamorphosed magma intrusions and basic rocks with meta-tuff sometimes interspersed with gneiss and mica schist in bands and lenses.
[2] Geographic locations of major formations discussed. Modified from N.R. McKenzie et al. (2011). 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).
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]
Location: the tectonic contact between the (autochthonous) Western Gneiss Region and rocks of the (allochthonous) Blåhø nappe on Otrøy, Caledonides, Central Norway. A mylonite (through a petrographic microscope) showing rotated so-called δ-clasts. The clasts show that the shear was dextral in this particular cut.
Thin section of garnet mica schist from Salangen, Norway. A garnet porphyroblast (black) contains curved trails of small inclusions (white and grey). Some garnet porphyroblasts contain curving trails of quartz and other mineral inclusions that record rotation of the crystals relative to their surroundings.
[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 ...