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In cross section they have the shape of an eye. [1] Feldspar, quartz, and garnet are common minerals which form augen. [2] Augen form in rocks which have undergone metamorphism and shearing. The core of the augen is a porphyroblast or porphyroclast of a hard, resilient mineral such as garnet.
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.
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]
Gneiss, a foliated metamorphic rock. Quartzite, a non-foliated metamorphic rock. Foliation in geology refers to repetitive layering in metamorphic rocks. [1] Each layer can be as thin as a sheet of paper, or over a meter in thickness. [1] The word comes from the Latin folium, meaning "leaf", and refers to the sheet-like planar structure. [1]
The abbreviation is not always a short form of the word used in the clue. For example: "Knight" for N (the symbol used in chess notation) Taking this one stage further, the clue word can hint at the word or words to be abbreviated rather than giving the word itself. For example: "About" for C or CA (for "circa"), or RE.
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 optically flat.
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.