Search results
Results from the WOW.Com Content Network
The British Geological Survey (BGS) and the International Union of Geological Sciences (IUGS) both use gneiss as a broad textural category for medium- to coarse-grained metamorphic rock that shows poorly developed schistosity, with compositional layering over 5 millimeters (0.20 in) thick [2] and tending to split into plates over 1 centimeter ...
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.
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.
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.
A centerpiece section contained a feature puzzle or puzzles, such as puzzles from the World Puzzle Championship or the annual Lt. Nodumbo puzzle mystery. Until the July 2009 issue it contained a contest in every issue, most often a variety crossword or trivia quiz, and the contest resumed upon the Games merger.
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.
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
Main page; Contents; Current events; Random article; About Wikipedia; Contact us; Donate