Geology And Geophysics

Gneiss is a Type of Foliated Metamorphic Rock that is very Hard and Similar to Granite



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In dialectological terms, the word gneiss was coined from the German verb, gneist, a reference to glittering rock. Some other authorities claim that gneiss was actually an old Anglo-Saxon mining expression applied on worthless or valueless material or object. In physical terms gneiss refers to one type of the two resultant rock formations that are formed as a result of metamorphic action on igneous rocks. This is a type of foliated metamorphic rock that is very hard and similar to granite, but not actually, however could be used as such as well as in other applications. Pronounced as “nice”, gneiss usually has light layers of quartz and feldspar, or dark layers of hornblende and biotite running through it.  

Ideally, rocks consist of several minerals, some of which are essential for the quality and type of the rock, while some of the mineral components are just accessories that came to be by the way. This explains why a rock is classified as a mineral resource.  Each rock type was formed under certain specific conditions, resulting in the formation of a fairly predictable group of minerals. In physical terms gneiss refers to one type of the two resultant rock formations that are formed as a result of metamorphic action on igneous rocks. Ideally, rocks normally consist of several minerals, some of which are essential for the quality and type of the rock, while some of the mineral component are just accessory that came to be by the way. A rock may be thought of as a "mineral environment. Each rock type was formed under certain specific conditions, resulting in the formation of a fairly predictable group of minerals.  

Geology is the study of the structures that made up the earth, most especially those structures that are easily visible to man such as rocks, stones, sands, soil types as well as other structures and minerals and valuable metal resources and components embedded under the surface of the earth and other mineral resources that protrude from beneath the ground into the surface. Geology covers a very wide scope in time and space, encompassing some aspects of the whole world and its broad and very old history. Geology deals with the evolution of rocks and continents and the evolution of life, time and the structures of the earth. Through the scientific school of thought called geology, we are able to study the history, the origins, the formation as well as the composition of various structural and mineral resources, as well as the expanse and extent of such structures with a view to make mankind fully benefit from them as much as possible. Those common physical structures generally called rocks produce what is known as gneiss. Rocks are either buried in the ground, or protrude up above the ground, in terms of big stones, hills and mountains. However, unlike ores or metals, rocks are much less definite in their composition. But, in general terms, we have three classifications of rocks. These are igneous rocks, sedimentary rocks, and metamorphic rocks. Gneisses are typical types of rocks under the class or categories of metamorphic rocks that are formed by the resultant effects of regional metamorphosis, that is, a complete or marked change of the structure in physical form, structural content, and substance value. There could also be changes in appearance or character, and general transformation. By virtue of the essential process of metamorphosis, sedimentary or igneous rocks that lied buried deeply underneath the earth, and subjected to very high temperature and pressure over a long period of time, are transformed to gneiss. The transformation and the marked effect of changes that took place will wipe off the original features of the old structure to bring forth a completely new structure or re-crystallized composition. Nevertheless, the geochemical traces and historical properties of gneiss are usually traceable through scientific studies, thereby providing us the resources with which to find out about the past of these elements as well as the entire paleontological, petrologic, and stratigraphic properties of the environment and the elements within the neighborhood and its vicinity.  In essence of this, mankind is provided with the tools with which to study and determine the gneiss’ past history and properties as well as a good guide of past lives and archeological existences.

As earlier mentioned, normal rock types called igneous rocks undergo metamorphosis to form metamorphic rock types. However, the metamorphic rock types produced are of two types – Gneiss and Schist. Gneiss is coarsely crystalline, with the crystals streaked out typically in one direction. In general, gneiss is characteristic of the type of formation whereby thin foliate layers are embedded at intervals within the structure, but without fracture along the plains of the mineral streaks and thicker veins of minerals with large grains. This distinctively differentiated gneiss from schist, which is more strongly aligned and more evenly layers in terms of appearance. The schist rock types are finely crystalline, mostly with more plentiful mica component, and splitting in thin flakes and sheets.

Further metamorphic occurrences would later transform gneiss rocks first into migmatite, and finally into granite. Gneiss rock types are the most common, and they make up the largest of the sold outer layer of the Earth. This made it possible to find them everywhere from one continent to another, and from one country to another country. As a result of regular or continuous metamorphic action, gneiss rocks comes in form of medium-foliated types to coarse-foliated rock types which are often re-crystallized bearing small proportions of other minerals such as micas, chlorite, etcetera. It is the re-crystallization and the mineral component in gneiss that determines the name given to various gneiss types. Gneiss that was formed from an igneous rock is called orthogneiss. The gneiss rock that is formed from sedimentary rock is called paragneiss. Rocks that have some properties or elements similar to that of the gneiss rock are called gneissose.

Generally, rocks are valuable and vital components in our lives. Hills, rocks and mountains have served as watch posts against enemies and their attacks in the past. Caves and grottos had been used many a times as hiding places against invading enemies, and from other forms of attacks. Because gneiss are a type of metamorphic rock with uneven granular medium to coarse grained crystalline with varied degree of mineral bearings, its general application in buildings, construction and civil engineering works is unique. Gneiss have always served mankind in road construction and general building works. The colors of gneiss rocks are variable, and as a result of this as well as its chemical and physical properties, some gneisses are used in the place of granites and as other building stones, while majority are applied for structures and structural purposes. It is a common feature to come across the generous applications of gneisses in various forms of flooring, steps and staircases, as facing stones or slabs in adequate building points and locations in preference to tiles; as ornamental stones to add value and aesthetics to the visible parts of buildings and monuments; as work surfaces such as front office desks, stands, dividers and executive tables, desks, stands or just decorations in the offices and corporate places. At home, gneisses are applied as water stands in the bathrooms and kitchen as well as part of the essential structures within the living apartment and the dining and sitting rooms. The graveyards are well known for generous application of gneiss in various colors, shapes and sizes for tombs as well as for the grave and its decorations.

The excavation and quarrying of gneiss for adequate process and for our general use is undertaken by miners.

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