Dana Classification of Minerals

Classification of Minerals: 

Minerals may be classified according to chemical composition. They are here categorized by anion group. The list below is in approximate order of their abundance in the Earth’s crust. The list follows the Dana classification system.
Silicate Class
The largest group of minerals by far are the silicates (most rocks are >95% silicates), which are composed largely of silicon and oxygen, with the addition of ions such as aluminium, magnesium, iron, and calcium. Some important rock-forming silicates include the feldspars, quartz, olivines, pyroxenes, amphiboles, garnets, and micas.
Carbonate Class 
The carbonate minerals consist of those minerals containing the anion (CO3)2- and include calcite and aragonite (both calcium carbonate), dolomite (magnesium/calcium carbonate) and siderite (iron carbonate). Carbonates are commonly deposited in marine settings when the shells of dead planktonic life settle and accumulate on the sea floor. Carbonates are also found in evaporitic settings (e.g. the Great Salt Lake, Utah) and also in karst regions, where the dissolution and reprecipitation of carbonates leads to the formation of caves, stalactites and stalagmites. The carbonate class also includes the nitrate and borate minerals.
Sulfate Class
Sulfates all contain the sulfate anion, SO42. Sulfates commonly form in evaporitic settings where highly saline waters slowly evaporate, allowing the formation of both sulfates and halides at the water-sediment interface. Sulfates also occur in hydrothermal vein systems as gangue minerals along with sulfide ore minerals. Another occurrence is as secondary oxidation products of original sulfide minerals. Common sulfates include anhydrite (calcium sulfate), celestine (strontium sulfate), barite (barium sulfate), and gypsum (hydrated calcium sulfate). The sulfate class also includes the chromate, molybdate, selenate, sulfite, tellurate, and tungstate minerals.
Halide Class
The halides are the group of minerals forming the natural salts and include fluorite (calcium fluoride), halite (sodium chloride), sylvite (potassium chloride), and sal ammoniac (ammonium chloride). Halides, like sulfates, are commonly found in evaporitic settings such as playa lakes and landlocked seas such as the Dead Sea and Great Salt Lake. The halide class includes the fluoride, chloride, and iodide minerals.
Oxide Class
Oxides are extremely important in mining as they form many of the ores from which valuable metals can be extracted. They also carry the best record of changes in the Earth’s magnetic field. They commonly occur as precipitates close to the Earth’s surface, oxidation products of other minerals in the near surface weathering zone, and as accessory minerals in igneous rocks of the crust and mantle. Common oxides include hematite (iron oxide), magnetite (iron oxide), chromite (iron chromium oxide), spinel (magnesium aluminium oxide – a common component of the mantle), ilmenite (iron titanium oxide), rutile (titanium dioxide), and ice (hydrogen oxide). The oxide class includes the oxide and the hydroxide minerals.
Sulfide Class
Many sulfide minerals are economically important as metal ores. Common sulfides include pyrite (iron sulfide – commonly known as fools’ gold), chalcopyrite (copper iron sulfide), pentlandite (nickel iron sulfide), and galena (lead sulfide). The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, and the sulfosalts (sulfur and a second anion such as arsenic).
Phosphate Class
The phosphate mineral group actually includes any mineral with a tetrahedral unit AO4 where A can be phosphorus, antimony, arsenic or vanadium. By far the most common phosphate is apatite which is an important biological mineral found in teeth and bones of many animals. The phosphate class includes the phosphate, arsenate, vanadate, and antimonate minerals.
Element Class
The Elemental group includes metals and intermetallic elements (gold, silver, copper), semi-metals and non-metals (antimony, bismuth, graphite, sulfur). This group also includes natural alloys, such as electrum (a natural alloy of gold and silver), phosphides, silicides, nitrides and carbides (which are usually only found naturally in a few rare meteorites).
Organic Class:
The organic mineral class includes biogenic substances in which geological processes have been a part of the genesis or origin of the existing compound. Minerals of the organic class include various oxalates, mellitates, citrates, cyanates, acetates, formates, hydrocarbons and other miscellaneous species.Examples include whewellite, moolooite, mellite, fichtelite, carpathite, evenkite and abelsonite.

Properties of Minerals

Properties of Minerals

According to Nickel E.H. Of 1995,"A mineral is either a chemical compound or an element, usually found in the crystalline structure, which is an outcome of the ecological course of action” . According to O’Donoghue of 1990, Minerals occur in nature as substances that are inorganic, Their chemical composition and physical properties are predictable and exact”. According to Mason et al of 1968,“A mineral occurs in nature as a solid that is homogenous and formed inorganically, Its chemical composition is exact with a disciplined orientation of its atoms”. According to Sinkankas of 1966 “Each mineral has its own properties by which it is discriminated from one another. These discrete properties occur in accordance with their type of atom and their configuration within the element. According to Dana & Ford of 1932,”A mineral is a substance composed of naturally occurring inorganic processes that have a precise chemical composition, combined under ideal circumstances, along with its physical properties, assurance of its traits is conveyed by its crystalline structure.  According to Brush & Penfield of 1898, each distinctive chemical compound that occurred in nature inorganically with a precise orientation of its molecular structure or the order of crystallization and clearly specified physical properties, makes the variety of mineral” Minerals- Physical Properties Mineralogists identify a particular specimen of mineral with the help of its physical properties. It is possible to conduct certain tests where it is obtained, whereas many other tests are needed with special laboratory equipments. For a beginner in geology, many simple tests are available, which results in a high level of precision. The series of tests are performed in a systematic manner, starting from ordinary experiments and observing the results leading to more intricate tests. Mineral Properties  A mineral is identified by the aforesaid physical properties: Magnetism Hardness Tenacity Color Odor Luster Taste Streak Specific Gravity Cleavage of Fracture Diaphaneity or Transparency value Crystalline structure The properties of every mineral are clearly described as follows: Detailed Description of mineral properties Color The majority of the minerals possesses distinct color by which they are identified. The minerals that are opaque have a tendency of consistency in their color.. The color variations of the transparent to translucent minerals are vast on account of the trace minerals present in it. Hence we cannot depend on color as a measure of identifying their properties. Streak The pulverized mineral color is called a streak. This displays the exact minerals exact color. In bulk solid structure, the trace mineral color changes with light reflection in a particular form. The powdered constituents of a streak of the trace minerals induce a minute effect on the reflecting light. The streak in metallic minerals is inclined to seem deeper in color on account of the absorption of the reflecting light on the small streak constituents. The constituents that are not metallic have an inclination to reflect the majority of light and thus they look a paler color or more or less white. The streak is very precise in illustrating the mineral’s color. The streak offers a highly dependable property of the mineral when compared to color discrimination. Hardness Minerals are better identified by their hardness. Hardness represents the property by which it is possible to measure the resistance of the mineral to scratching. This is checked on the Mohs scale that has 10 sets of minerals with known hardness. Talc, which is the softest of the minerals, has a Mohs rating of 1. The rating of Diamond which represents the hardest of the mineral is ten. Harder minerals are used to scratch softer minerals, since their binding force is weaker, which the mineral that is harder, can easily break. Fracture & Cleavage When struck with force, there is a tendency for the minerals to shear along smooth surfaces or along the lines. The fractures of various types of minerals are diverse which exhibits varied cleavage patterns. Two different criteria sets are used to define cleavage. The quickness of obtaining cleavage is explained by the primary criteria set. If cleavage is attained with ease, it is regarded as perfect. Besides, its cleavage planes appear conspicuous. If in case cleavage is acquired with difficulty, it is regarded as excellent, provided you have clear cleavage planes. In conclusion, it is regarded as imperfect in case cleavage is attained with complication and certain planes are not easily identified. The track of the surface cleavage is obtained by the second criteria set. According to the cleavage surface’s form, there are named as Rhombohedral, Cubic, Dodecahedral, Octahedral, Prismatic or Basal. It is the particular cleavage lines, angles that give the definition of the criteria. Cleavage Type Angles Cubic cleaves appear @ 90o to each other in three directions, the Rhombohedral type also cleaves in 3 directions, but do not achieve 90o to each other, Octahedral cleaves in 4 directions, Dodecahedral cleaves in 6 directions, Basal in 1 direction and Prismatic in 2 directions. The class of cleavage surface is determined by the fracture of the mineral. The majority of minerals exhibit either grainy or uneven fracture, hackly fracture (rough, jagged) or Conchoidal fracture (curved, lines like a shell). Crystalline Structure  The crystals of mineral are formed in different sizes and shapes, according to the orientation of the molecules, ions or atoms; it is possible to specify a crystal shape and their bonding. Such an arrangement is what crystal lattice is. The crystalline structure occurs in different degrees, where the crystal fibers become complicated or rather difficult to glance with your naked eye, and difficult even by using a hand lens. It is possible to have a view of the Crystalline and Microcrystalline structures only through powerful magnification. Minerals with no definite crystalline structure are called amorphous. But the number of amorphous crystals is limited which are viewed only by using very high magnification. Diaphaneity (Transparency) The capacity to permit light to traverse through it or the transparency percentage of a mineral is called Diaphaneity, which varies according to the mineral’s thickness. Tenacity The property by which the particle is bonded in the mineral is called tenacity or otherwise it is the resistance of the particles in a mineral to separate.  Magnetism A mineral’s property to repel or attract materials that are magnetic is called magnetism. It is cumbersome to identify the magnetic strength of different minerals, however, having a knowledge of the dissimilarities is an asset. Luster An indication of the extent to which a mineral’s surface reflects light is the property of the mineral called luster. The shine of the mineral is influenced by the light’s brightness with which one views the surface of the mineral. Metallic property means, opacity of the mineral in nature and reflects light just like metals do. Sub-metallic property means the mineral appears dull, opaque and dark in color. Nonmetallic means the mineral never reflects light just like metals do. Modifiers which represent the general qualities are used to illustrate nonmetallic minerals. Waxy minerals resemble wax or paraffin. Vitreous minerals resemble shattered glass. Pearly minerals resemble oil poured on water. The resinous mineral resembles the resin of tree sap that is hardened. Adamantine mineral resembles brilliance like the diamond. Odor The majority of minerals occurred in nature are odorless, except when they are either heated, moistened or rubbed against something. Taste Only minerals that are soluble possess taste; however, it is imperative that minerals are never placed either on the tongue or in the mouth. Neither should you test this quality in your classroom Density (Specific Gravity) A mineral density or specific gravity is a relation of the ratio of its weight to the mass of the same quantity of water. By determining the difference in weights of mineral in water and the same quantity in the air, it is possible to find the weight of the same quantity of water.

Contact Metamorphism

Contact metamorphism is the name given to the changes that take place when magma is injected in     the surrounding solid rock (country rock). The changes that occur are greatest wherever the magma comes into contact with the rock because the temperatures are highest at this boundary and decrease with distance from it. Around the igneous rock that forms from the cooling magma is a metamorphosed zone called a contact metamorphism aureole. Aureoles may show all degrees of metamorphism from the contact area to unmetamorphosed (unchanged) country rock some distance away. The formation of important ore minerals may occur by the process of metasomatism at or near the contact zone.

Magma Intruded into Country Rock

Contact Metamorphism

Contact metamorphic rocks

Amphiboles occur in contact metamorphic aureoles around igneous intrusions. (An aureole is the zone surrounding an intrusion, which is a mass of igneous rock that solidified between other rocks located within the Earth.) The contact aureoles produced in siliceous limestones and dolomites, called skarns or calc-silicate rocks, characteristically contain metamorphic amphiboles such as tremolite or actinolite. The presence of tremolite implies a relatively low grade of metamorphism as tremolite breaks down to form the pyroxene diopside in the presence of calcite and quartz at elevated temperatures. Richterite-winchite occurs in hydrothermally metamorphosed limestones. Magnesium-rich anthophyllites are found along contact zones of granitic dikes intruding ultramafic rocks (those rich in iron and magnesium).

Contact Aureole

When a rock is contact altered by an igneous intrusion it very frequently becomes more indurated, and more coarsely crystalline. Many altered rocks of this type were formerly called hornstones, and the term hornfels is often used by geologists to signify those fine grained, compact, non-foliated products of contact metamorphism. A shale may become a dark argillaceous hornfels, full of tiny plates of brownish biotite; a marl or impure limestone may change to a grey, yellow or greenish lime-silicate-hornfels or siliceous marble, tough and splintery, with abundant augite, garnet, wollastonite and other minerals in which calcite is an important component. A diabase or andesite may become a diabase hornfels or andesite hornfels with development of new hornblende and biotite and a partial recrystallization of the original feldspar. Chert or flint may become a finely crystalline quartz rock; sandstones lose their clastic structure and are converted into a mosaic of small close-fitting grains of quartz in a metamorphic rock called quartzite.

The Purcell Sill with contact metamorphism in Glacier National Park, MT

If the rock was originally banded or foliated (as, for example, a laminated sandstone or a foliated calc-schist) this character may not be obliterated, and a banded hornfels is the product; fossils even may have their shapes preserved, though entirely recrystallized, and in many contact-altered lavas the vesicles are still visible, though their contents have usually entered into new combinations to form minerals that were not originally present. The minute structures, however, disappear, often completely, if the thermal alteration is very profound. Thus small grains of quartz in a shale are lost or blend with the surrounding particles of clay, and the fine ground-mass of lavas is entirely reconstructed.

Contact Metamorphism. The white band is a talc deposit in southern Death Valley, California. The
dark green rocks below the talc is diabase; the brown rocks above the talc is dolomite. The talc formed
by contact metamorphism of the dolomite by the intruding diabase.

Peneplain

What is Peneplain?

The peneplain (from the latin parene = almost, and plain) designates a wide almost uniform plain, with slight unevenness a prolonged erosion and the coalescence of watersheds, originated in a horizontal modeling product. It is a set of watercourses and watersheds of low altitude with regard to the valleys, with some residual reliefs along the basin of the rivers. The peneplain would therefore be the result of the last stage of the geographical cycle produced by the river waters.This concept was developed by early geomorphologists, William Morris Davis and Walther Penck, at the beginning of the 20th century. Serious objections, an orogeny that has happened a prolonged phase of tectonic stability without the rejuvenation of the relief that would have allowed the normal development of the geographical cycle.After millions of years, the valley bottom plane are expanding more and more, joining with each other and finally forming a huge surface almost flat, that receives the name of peneplainsPeneplain is a concept that is frequently used in the field of geography. The term is used to name a surface similar to the plain, although with small elevations that interrupt the plain. The physiognomy of the peneplain depends on the consequences of erosion.Arguably, therefore, that a peneplain is a plain which lacks uniformity due to the action of erosion and hydrography, resulting in the formation of certain reliefs. The peneplain can be formed from the union of valleys, with over millions of years, giving place to a large quasi-flat terrain.The peneplain development involves the completion of a cycle of erosion, in which the reliefs are destroyed and remains almost flat with little elevation with respect to its base level.Elements that tend to form the peneplains are the remains of large rock formations which, due to the actions of the agents of erosion, lost lift. So that the process is carried out, needed an extended temporary period lacking interference; otherwise, the cycle is interrupted and the ground could achieve its rejuvenation.It is possible to find peneplains in various regions of the world. In Extremadura, an autonomous community of Spain, the peneplain dominates much of the territory. Castilla y León, another Spanish community, also has vast peneplains. In Latin America, Venezuela has peneplains in the region of Guayana, 

Concept of Peneplain:
Landform that usually occupy large tracts and, due to erosion, presenting a surface gently undulating, without hardly a difference in height between the valleys and the watersheds. It consists of old and eroded materials.In temperate countries are recognized by the regularity of the surfaces, the watersheds have all the same altitude, the valleys have carved back these peneplains dating back to the tertiary. Training corresponds to the end of the cycle of erosion which is completed with the total destruction of the reliefs with the result of a monotonous relief and little raised above the base level.In Spain are located in the western part of the submeseta norte. The Extremadura peneplain is a great extension that has between 300 and 500 metres above sea level and consists of a Paleozoic base traversed by the Guadiana river.

Possible peneplain surface on granite, Heaphy Track area

Source: https://ncealevel2sci.wikispaces.com/

Introduction of Geology

What is Geology?

Geology is the study of the Earth, the materials of which it is made, the structure of those materials, and the processes acting upon them. It includes the study of organisms that have inhabited our planet. An important part of geology is the study of how Earth’s materials, structures, processes and organisms have changed over time.

What Does a Geologist Do?

Geologists work to understand the history of our planet. The better they can understand Earth’s history the better they can foresee how events and processes of the past might influence the future. Here are some examples: Geologists study earth processes: Many processes such as landslides, earthquakes,floods and volcanic eruptions can be hazardous to people. Geologists work to understand these processes well enough to avoid building important structures where they might be damaged. If geologists can prepare maps of areas that have flooded in the past they can prepare maps of areas that might be flooded in the future. These maps can be used to guide the development of communities and determine where flood protection or flood insurance is needed. Geologists study earth materials: People use earth materials every day. They use oilthat is produced from wells, metals that are produced from mines, and water that has been drawn from streams or from underground. Geologists conduct studies that locaterocksthat contain important metals, plan the mines that produce them and the methods used to remove the metals from the rocks. They do similar work to locate and produce oil, natural gas and ground water. Geologists study earth history: Today we are concerned aboutclimate change. Many geologists are working to learn about the past climates of earth and how they have changed across time. Thishistorical geology news information is valuable to understand how our current climate is changing and what the results might be. 

Geology as a Career: 

 Geology can be a very interesting and rewarding career. The minimum training required is a four-year college degree in geology. Pre-college students who are interested in becoming geologists should take a full curriculum of college preparatory courses, especially those in math, science, and writing. Courses related to computers, geography and communication are also valuable. Share this: