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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]
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 ...
In some of the Blue Ridge Mountains occurrences, an epidotized augen gneiss is present exhibiting foliation structures. The dominant green epidote in unakite rocks is the metasomatic alteration product of plagioclase feldspar, while the orthoclase and quartz crystals remain unaffected.
Location: the tectonic contact between the autochthonous Western Gneiss Region and rocks of the allochthonous Blåhø nappe on Otrøy, Caledonides, Central Norway. Augen mylonite from near Røragen, Norway. This deformed megacrystic granite has large alkali felspar and small plagioclase feldspar porphyroclasts. Sample 18 cm x 10 cm.
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).
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.
In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron microprobe. A thin sliver of rock is cut from the sample with a diamond saw and ground
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.