Petrology and structure of gneiss anticlines near baltimore, maryland. Of these, gneiss is a metamorphic rock type, which is characterized by dark and light colored minerals including feldspar and quartz. How can a schist can be transformed to augengneiss. See more ideas about rocks and minerals, geology and rocks and gems. It is formed by the metamorphosis of granite, or sedimentary rock. Baltimore county, maryland, july 15, 1989 george w.
Augen, meaning eyes, is a coarsegrained gneiss resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shearbound feldspar. The lighter bands contain mostly quartz and feldspar, the darker often contain biotite, hornblende, garnet or graphite. Rock specimens are useful for studying textures, grain sizes, and other features altered by pressure, temperature, and other natural forces. During regional metamorphism a granitic augen gneiss can be transformed into a. Although many gneisses are quartzofeldspathic, the mineral composition is not an. The term gneiss is not only the name of a particular kind of metamorphic rock, but also, in a wider sense, it is used as an expression of a certain texture. Thus when we use gneiss as a name in the limited sense, we mean a rock which has the composition of granite quartz, feldspar, and mica with a certain foliated texture. The exposure is about 180 miles north of the town of yellowknife in canadas northwest territories. Minerals free fulltext an alternative source for ceramics and. Composition ranges from tonalite to granodiorite to quartz monzonite. Original paper geological position and origin of augen. Gneiss, metamorphic rock that has a distinct banding, which is apparent in hand specimen or on a microscopic scale.
Pink and gray with good banding and lenticular potassium feldspar eyes. Augen gneiss is a variety containing large eye shaped grains augen of feldspar. The rocks that form gneiss are exposed to extreme pressures and temperatures of between 600 and 700 degrees celsius. Norway 361 v gneiss d mllioy group including sparagrritic rocks o 5 kms. A foliated rock formed by regional metamorphism, in which bands or lenticles of granular minerals alternate with bands or lenticles in which minerals having flaky or elongate prismatic habits predominate. Gneiss definition and meaning collins english dictionary.
Granite gneiss definition is a rock consisting of an orthogneiss or paragneiss having the composition of a granite. Gneiss definition, a metamorphic rock, generally made up of bands that differ in color and composition, some bands being rich in feldspar and quartz, others rich in hornblende or mica. Reconnaissance studies of gneisses, ultrabasites, eclogites and. Gneiss is a very widespread rock type, especially in the lower parts of the continental crust, but it is also a common rock on the surface in some places scandinavia, canada, and other shield areas where crystalline rocks are not covered by a layer of sedimentary rocks.
Generally, less than 50% of the minerals show preferred parallel orientation. Feldspar augen, borded by biotite, in a deformed graundmass in a gneiss. The henderson gneiss is a mediumgray, biotite granite augen gneiss, which is composed of microline, oligoclase, quartz, biotite, and minor amounts of muscovite, epidote, and titanite. The disposition of the augen gneiss bodies is concordant. This type of gneiss gains its name from the elliptic or lensshaped form of many of its mineral grains.
Geological position and origin of augen gneisses from the policka. Feldspar, quartz, and garnet are common minerals which form augen. Gneiss definition is a foliated metamorphic rock corresponding in composition to a feldspathic plutonic rock such as granite. Gneiss gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It should also be remarked that the essential component minerals of the rocks of this family are practically always determinable by naked eye inspection or with the aid of a simple lens. Gneiss is a very widespread rock type, especially in the lower parts of the continental crust, but it is also a common rock on the surface in some places scandinavia, canada, and other shield areas where. Structure, stratigraphy and magnetic susceptibility of. It is this banded appearance and texture rather than composition that define a gneiss.
Development of an augen gneiss terrain springerlink. Esmond igneous suite augen granite gneiss pale to darkgray, medium to coarsegrained, granite gneiss characterized by large feldspar porphyroclasts 1 cm. Although many gneisses are quartzofeldspathic, the mineral composition is not an essential factor in its definition american usage. Rotation of augen during growth, due to shearing, leads to sigmoidal inclusion trails and augen tails at different levels in the external foliation. Gneiss displays distinct foliation, representing alternating layers composed of different minerals. Quick navtop about augen gneiss classification subdivisions mineralogy pronounciation internet links mineral andor locality is an outreach project of the hudson institute of mineralogy, a. The most common path begins with shale, which is a sedimentary rock. The distinctive textures and homogenous geochemistry of augen. The joshimath formation consists of biotite augen gneiss, kyanitesillimanite gneiss, and kyaniteaugen gneiss. The gneiss family of rocks varieties, uses and mineral make up. Unlike schist, however, gneiss does not readily cleave along these parallel layers. These temperatures cause the individual minerals to migrate, forming distinct bands through the rock.
Different select categories of rock specimens are available for purchase as well, including metamorphic, igneous, and sedimentary rocks. When large felspars, of rounded or elliptical form, are visible in the gneiss, it is said to have augen structure ger. Although a gneiss is commonly feldspar and quartzrich, the mineral composition is not an essential factor in its definition. F elongate enclaves of thinly layered tonalitic gneiss containing a 3730 ma zircon population enclosed within 3300 ma augen gneiss, eastern side of the jack hills. Augen gneiss henderson augen gneiss augen gneiss, from the german. In most other regards, gneiss is quite various and, therefore, is often named based on certain characteristics, such as parent material or mineral constituents, in order that samples of the. It is characterised by a layered appearance caused by the minerals from quartzo. Typical modal mineralogy is 2030 percent quartz, 020 percent kfeldspar, 3080 percent plagioclase, 015 percent biotite typically chloritized, and 06 percent white mica. Study of the structural state and composition of feldspars of the bedford augen gneiss, new york hipple, dennis l on.
The distinctive textures and homogenous geochemistry of augen gneisses make them a potentially useful lithological marker in a geological reconstruction of e and ne parts of the bohemian massif. Augen gneiss, from the german augen, meaning eye, is a coarsegrained gneiss, interpreted as resulting from metamorphism of granite, which contains characteristic elliptic or. During this transformation, clay particles in shale transform into micas and increase in size. Granulitefacies rocks in the whatley mill gneiss, pine. Choose from 10 different sets of gneiss flashcards on quizlet.
Regional metamorphism can transform shale into slate, then phyllite, then schist, and finally into gneiss. As further reading, i recommend the excellent book by ron h. Gneiss definition in the cambridge english dictionary. Gneiss is a medium to coarsegrained banded rock formed as a result of high grade regional metamorphism. Five star interactive notetaking composition book, 1 subject, college ruled composition. Gneiss has been defined as a foliated rock formed by regional metamorphism in which granulose bands or lenticles of granular minerals alternate with schistose bands and lenticles of flaky or elongate. Xpl image, 2x field of view 7mm feldspar augen in a deformed graundmass in a gneiss.
Augen gneiss and quartzofeldspathic gneiss have similar chemical compositions, but augen gneiss seems to be somewhat more mafic. Granitegneiss definition of granitegneiss by merriamwebster. The composition of augen gneiss is more mafic than average continental shield surface rock and less mafic than the average crustal rock. Injection gneisses are formed by injection of veinlets of granitic material into a schist or some other foliated rock. Quick navtop about augen gneiss classification subdivisions mineralogy pronounciation internet links mineral andor locality is an outreach project of the hudson institute of mineralogy, a 501c3 notforprofit organization. Some, such as augen gneiss, are also described based upon their structure.
Pencil gneiss contains rodshaped individual minerals or segregations of minerals, and augen gneiss contains stubby lenses of feldspar and quartz having the appearance of eyes scattered through the. When minerals, rocks, and fossils cannot be accurately identified by macroscopic observation and testing, thin section slides can. Structure, age, and regional significance of syntectonic. Wards gneiss augen specimens rock specimens rock thin sections when minerals, rocks, and fossils cannot be accurately identified by macroscopic observation and testing, thin section slides can reveal the composition and structure of the specimens on a microscopic level. G coarsegrained tonalitic gneiss with a distinctive streaky texture of smeared biotite aggregates and containing a dominant c. Gneiss is a foliated metamorphic rock identified by its bands and lenses of varying composition, while other bands contain granular minerals with an interlocking texture. Igneous and metamorphic rocks under the microscope. The ancient gneiss is named after the acasta river, located east of great bear lake, where the outcrop was first found in the 1980s. It is characterized by alternating light and dark bands differing in mineral composition coarser grained than schist. Evolution of a granite gneissmigmatite terrane in rajasthan. Feldspar, quartz, and garnet are common minerals which form augen augen form in rocks which have undergone metamorphism and shearing. Hand samples of augen gneiss supplied in a white card tray with a label. Gneiss is a medium to coarsegrained, semischistose metamorphic rock. Augen from german eyes are large, lenticular eyeshaped mineral grains or mineral aggregates visible in some foliated metamorphic rocks.
The whatley mill gneiss is the most voluminous exposure of the pine mountain basement massif in eastern alabama. Gneiss, a term long used by the miners of the harz mountains to designate the country rock in which the mineral veins occur. Gneiss usually is distinguished from schist by its foliation and schistosity. Some, such as augen gneiss, are also described based upon. Hornblende gneiss gneiss is a widespread metamorphic rock that is medium to coarse grained and often contains significant amounts of quartz and feldspar.
Volume gain during shearing of the whatley mill gneiss, pine. Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. Spatial association with augen gneiss mdag and igneous composition implies a plutonic origin for this rock type. A wide range of minerals are important as accessories and are characteristic either of the protolith composition or metamorphic grade. Augen gneiss is a foliated metamorphic rock with large crystals of lenticular or. Dimensional parallellism of prismatic and bookformed minerals. Geochemical characteristics of granitoids ho gneiss from. Avery zweckform notizo 7043 notebook bound soft cover a4 squared 80 sheets red. Fig, l simplified map of the glomfjord region showing general relation of the meloy group to the gra. Kfeldspar bearing augen gneisses by a model of infiltra. It is formed by the metamorphosis of granite, or sedimentary. An essentially undeformed dyke of nattaung granite cutting augen gneiss has a zircon upb. Its type lithology is a protomylonitic gneiss composed of kspar augen, up to 5 cm. The granite gneiss and migmatitic terrane of southcentral rajasthan around devgarhmadariyaanjana areas in rajsamand district has been geologically mapped and is found to contain rocks of.
The zimithang granite is a grey to pink coloured porphyroclastic augen gneiss, foliated and partly undeformed monzo to syenogranitic in composition and crops out as a large batholith emplaced in. Its type lithology is a protomylonitic gneiss composed of kspar augen, up to 5 cm in diameter, in a finer matrix of biotite, microcline, and quartz. The gneiss family of rocks varieties, uses and mineral. True granites are present, but the augen gneisses are dominated by rather mafic, heterogeneous rocks of commonly quartz monzonitic composition. Orthogneiss is formed by the metamorphism of igneous rocks. Gneiss does not have any particular mineral composition, and the term refers only to the banded texture. Augen gneiss is a general term for gneissic rocks con taining oval or lenticular. Augen gneisses and related migmatites commonly form extensive areas in deep crystalline terrains and are interlayered with horizons of undoubted metasedimentary rocks. Augen gneiss, from the german augen, meaning eye, is a coarsegrained gneiss, interpreted as resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear bound feldspar porphyroclasts, normally microcline, within the layering of the quartz, biotite and magnetite bands. Landscape mode is not currently supported for this website. Other readers will always be interested in your opinion of the books youve read. A medium to coarsegrained rock, gneiss is primarily distinguished by its characteristic banding caused by the segregation of its mineral constituents. Pdf evolution of a granite gneissmigmatite terrane in.