Igneous rocks. Sedimentary rocks. Metamorphic rocks. The Rock Cycle. 2. Minerals – an Introduction. Definition of a mineral. Description of over Minerals from around the world minerals, aesthetic criteria such as size of cryml minerals and rocks, hydrothermally altered under. Rocks and Minerals. By Jan C. Rasmussen. (Revised from a booklet by Susan Celestian). Donations for reproduction from: Freeport McMoRan Copper.
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of Rocks. Page Use of Rocks and Minerals. Page Minerals. Page Classes of Rocks . the Earth's history. The analysis of rocks, minerals, and fossils. Texture refers to the physical appearance or character of a rock, such as grain size, shape, and arrangement. Igneous rocks that crystallize slowly beneath the. Earth Scientists: Nature Detectives. The Good Earth, Chapter 7: Rocks and Minerals. Are the rocks on. Mars the same as rocks on Earth?.
This rock basically shows evidence of the onset of partial melting in the lower continental crust, and if the process had gone further it would probably have been the source of a granite intrusion. Sedimentary Structures are another feature of sedimentary rocks that allows distinction between different rock units. These partially melted lower crustal rocks are also called migmatites. It grips you like some kinds of sinning; It twists you from foe to a friend; It seems it's been since the beginning; It seems it will be to the end. The elements from Oxygen to Magnesium make up The most characteristic feature is the so called slaty cleavage from newly formed micas. The origin of magmas has been a subject for considerable scientific debate in the first half of this century, but today it is basically agreed that three principal magma families see above can distinguished, basaltic, andesitic , and granitic , and that they are all the product of partial melting.
Hornblende crystals brown in a lava flow Mineral precipitation from solution: Malachite a copper carbonate precipitated in open spaces of a copper deposit. Each band marks a growth episode. A slice of a Tourmaline crystal. Shows growth zonation. Minerals can be classified into several groups according to their chemical composition. These groups are: If we for example consider the weight fractions of elements in the crust, it is obvious that.
These 9 minerals are all silicates , and are also called the rock forming minerals. They can be subdivided into two groups, the mafic and felsic minerals according to the principal rocks types they mainly occur in.
Mafic Minerals: The term mafic is used for silicate minerals, magmas, and rocks which are relatively high in the heavier elements dominated by Fe, Mg, Ca, Al, SiO2; Ma stands for magnesium and F stands for iron. The minerals are: Thus, mafic rocks are overall of dark color. Mafic magmas are usually produced at spreading centers, and represent material which is newly differentiated from the upper mantle.
Common mafic rocks include basalt and gabbro. Felsic Minerals: Felsic is a term used for silicate minerals, magmas, and rocks which have a lower percentage of the heavier elements, and are correspondingly enriched in the lighter elements, such as silica and oxygen, aluminum, and potassium. The most common felsic rocks are granite and rhyolite , which as we shall see later represent the end product of the Earth's crustal differentiation process.
Rocks that are intermediate in composition between these two groups are also called surprise! All of these minerals form through crystallization from silicate melts in the crust and mantle. I f we look at the composition of the 9 rock forming minerals, we see that they all belong into the silicate group of minerals.
The basic buildingstone of silicate minerals is the SiO 4 4- complex ion, the silica tetrahedron. Although we talk of the nine rock forming minerals, they are really families of minerals with the same structural styles in fact three of the rock forming minerals, albite, orthoclase, plagioclase are all from the feldpar family.
Despite the limited number of components, the large number of resulting silicate minerals have very distinct crystalline structures, and equally distinct physical and chemical properties. At first glance it may seem surprising that with a comparatively small number of components, and the silica tetrahedron as the dominant constituent, we can produce such a vast array of different compounds and structures.
But if you were to play with a box full of tetrahedrons, you would soon realize that tetrahedrons are very versatile geometrically , and allow the construction of many different shapes and structures. And indeed, the two elements are direct neighbors in the periodic system and thus show many parallels in their chemical behavior. The materials that the Earth's crust is made of are called rocks, and all rocks are made of minerals.
Minerals are to rocks what vegetables are to a salad. If you know what vegetables are in your salad, you can tell what kind of salad you have. Likewise, if you can identify the minerals in your rock, you can name it. Minerals are the fundamental unit for understanding rocks. Geologists distinguish three main groups of rocks with of course numerous subdivisions: Igneous Rocks are formed by the cooling and crystallization of a silicate melt dominated by oxygen and silicon, with a variety of other metals.
The occurrence and distribution of igneous rocks and igneous rocks types can be related to the operation of plate tectonics.
The molten rock material from which igneous rocks form is called magma. Magma is molten silicate material and may include already formed crystals and dissolved gases. The name magma applies to silicate melts within the Earth's crust, when magmas reach the surface they are referred to as lava.
Two Dissolved gases, CO 2 and H 2 O, are important even though they are not the most abundant components. The origin of magmas has been a subject for considerable scientific debate in the first half of this century, but today it is basically agreed that three principal magma families see above can distinguished, basaltic, andesitic , and granitic , and that they are all the product of partial melting.
They are rich in iron and magnesium and form through partial melting of the upper mantle from peridotite in areas of mantle upwelling and high heatflow mid-oceanic ridges; continental rifts. Andesitic Magmas are intermediate in composition between basalts and granites.
They form trough partial melting of subducted ocean crust in areas of crustal convergence subduction zones. In areas of island arc formation they are the dominant magma type. In areas of crustal compression and thickening subduction near continent they occur together with granitic magmas that originate in the lower crust. They originate in the lower crust in the deeply buried "root zones" of mountain belts.
In these areas the temperatures of deeply buried rocks become high enough to allow partial melting. The melts that form under these conditions are granitic in composition. Because of their lower temperature and high silica content granitic magmas tend to be highly viscous linked domains of silica tetrahedra , whereas basaltic magmas are of low viscosity much more fluid , and are able to flow Hawaii.
Andesitic magmas are in between these extremes. The various kinds of igneous rocks can be distinguished by mineral composition , chemical composition linked to minerals , and texture. Texture describes the way the minerals in the rock look like and relate to each other large vs small; ideal crystal shapes or irregular grains; etc. The resulting textures are called aphanitic fine grained , glassy and porphyritic if some crystals formed before extrusion.
Thus these textures are typical for volcanic rocks. Gas bubbles pressure drop at eruption may give rise to vesicular and frothy textures. Pyroclastic textures are found in volcanic rocks that formed from ashfalls and ashflows. Thus we see mainly phaneritic textures with minerals of coarse to intermediate grain size. If these rocks form at very shallow depths they may be called hypabyssal or subvolcanic rocks, and we may also see porphyritic textures e.
If they form at considerable depth they are called plutonic rocks and the respective rock bodies may be called stocks, or batholiths, or plutons.
Igneous Rocks and Mineral Composition. Name for Intrusive Rock This diagram shows the main groups of igneous rocks, their main mineral constituents and their intrusive cooling in the crust and extrusive cooling as lava flow equivalents. For example: Peridotite is the name for rocks of the upper mantle, and Komatiite is the name for extrusive lavas that are essentially of Peridotite composition.
The latter are found primarily in very old rocks Archean that formed soon after the formation of the first crust crust was thin, very mobile, and convection was vigorous. Different minerals crystallize at different temperatures olivine at high temperatures, quartz at low temperatures , and therefore the mineral composition of an igneous rock can tell us something about the cooling history of that rock.
Naming Bodies of Igneous Rocks.
Bodies of igneous rocks come in a large variety of shapes and sizes, and geologists use a variety of terms to describe these. A small sample of these terms is shown in the figure below. Volcanic Processes and Landforms. The processes which lead to the deposition of extrusive igneous rocks can be studied in action today, and help us to explain the textures of ancient rocks with respect to depositional processes.
Some of the major features of volcanic landforms and volcanic processes are summarized in the attached pages. Under heaven nothing is more soft and yielding than water. Yet for attacking the solid and strong, nothing is better; It has no equal. Sedimentary Rocks. Sedimentary Rocks are a product of the surface processes of the earth weathering, erosion, rain, streamflow , wind, wave action, ocean circulation.
The starting material for sedimentary rocks are the rocks outcropping on the continents. Processes of physical and chemical weathering break down these source materials into the following components: Sediments may form by: The probably most significant feature of sedimentary rocks is the fact that they are stratified , that means the sediments of any particular time period form a distinct layer that is underlain and overlain by equally distinct layers of respectively older and younger times.
Therefore sediments are the preserved record of former climates and landscapes. The study of sedimentary rocks allows therefore to look back in time and to decipher the sequence of events that made today's Earth what it is. In addition, because the animals that lived during these time periods are found preserved in their respective sediment units, a record of the animal and plant life is kept throughout Earth history.
This record allows us to see the changes of plant and animal communities through a time interval of more than 3 billion years 3. Stratification is also observed in sedimentary rocks from other planets, such as Mars sedimentary layers from Mars orbit , sedimentary layers at Mars surface. Because we can study them in the making, we probably know more details about the origin of sedimentary rocks, than that of igneous and metamorphic rocks combined. Several different types of sedimentary rocks can be distinguished according to mineral composition, and origin of the sediment.
The main groupings are: Depending on grain size they are subdivided into conglomerate grain size larger than 2 mm , sandstone size between 2 mm and 0. They usually occur as lenticular bodies that are interbedded with sandstones and sometimes mudstones. Conglomerates accumulate in stream channels mountain streams , along the margins of mountain ranges brought out by streams , and may also accumulate on beaches.
The source rock of a conglomerate can easily be determined by examining the lithology of the pebbles granite pebbles, basalt pebbles, etc. Because in many igneous and metamorphic source rocks the grain size of component minerals is larger than or equal to that of sandstones, it is much more difficult to determine the source rock of a sandstone as compared to a conglomerate.
The most abundant mineral in a sandstone is usually quartz , because it is the hardest one of the rock forming minerals and therefore the most resistant to abrasion during transport.
The second most abundant mineral is feldspar potassium feldspar , followed by micas. These minerals are also the chemically most stable under conditions of the Earth's surface among the rock forming minerals. The softer and less stable minerals hornblende, pyroxene, olivine are absent or at least fairly rare. Even though the mineral composition of a sandstone does not give us lots of direct clues as to the source rock composition, we can gain some insight into climate and transport history from the mineral composition of a sandstone.
The image at left shows a photomicrograph of a shale, taken at the same magnification as the photo of sandstone above. The grains are much finer now, the dark streaks are remains of organic matter, possibly they were films of algae or bacteria.
Chemical and Organic Sedimentary Rocks are the other main group of sediments besides clastic sediments.
They usually form by inorganic or organically mediated mineral precipitation, and as the result of biological activity. Usually it takes some special conditions for these rocks to form, such as small or absent clastic sedimentation would dilute chemical and organic input , high temperatures and high evaporation cause supersaturation [teakettle bottom], and high organic activity reefs, tropical swamps.
They consists predominantly of calcite CaCO 3 , and may form by inorganic precipitation as well as by organic activity. If looked at in detail, however, organic activity contributed practically all of the limestones in the geologic record.
Limestones may consist of gravel to mud sized particles, and thus classifications of limestones exist that are similar to those of clastic rocks. The picture at left shows a large colonial coral from a Tertiary coral reef in the Taiwan Strait. Growing over each other, the corals form a solid framework of carbonate skeletons.
Later the open spaces fill with carbonate cement and become solid bodies of limestone. Photomicrograph of ooid limestone. Grains are 0.
Large grain in center shows well developed concentric calcite layers. Ooids photo in upper left shows hand specimen of ooid limestone are the main form of inorganically precipitated carbonate and form limestones that look like layers of fish eggs.
A small fragment of carbonate e. Repetition of this process leads to multiple concentric layers. There is recent research that indicates that microorganisms may actually be involved in ooid formation, but more work needs to be done to firmly establish this. Even though dolomite can precipitate theoretically from seawater, it only rarely does, and probably most of the dolostones in the sedimentary record are due to post-depositional replacement of calcite by dolomite Mg for Ca exchange by Mg-rich pore waters.
They usually form from evaporation of seawater. They require high evaporation rates high temperatures for their formation, and usually the sedimentation basin has to be partially or totally closed off otherwise supersaturation not reached because of influx of new water. They usually indicate arid dry climate at their site of deposition.
Although they make only a small fraction of sedimentary rocks, they are important energy resources. Coal, for example is a carbonaceous rocks that consists of the altered due to increased pressure and temperature remains of trees and other plant material.
It has used since the last century for energy production and chemical industry. Oil shales are black mudstones that contain abundant organic matter that has been altered into solid kerogen or very viscous hydrocarbons bitumen that can be extracted from the rock through heating. Tar sands are sandstones whose pore spaces are filled with heavy crude oil and bitumen.
The hydrocarbons are usually extracted with steam. At current oil prices oil shale and tar sands are attracting interest because some occurrences are are reaching the point where exploitation becomes economically viable. It is likely that these more unconventional energy sources become more important as as oil supplies dwindle over the coming decades.
Sedimentary Structures are another feature of sedimentary rocks that allows distinction between different rock units. Sedimentary structures are a consequence of the depositional process at a site of deposition. The investigation of these structures in ancient rocks allows us to reconstruct physical conditions in the past , such as velocity and direction of depositing currents, emergent or submerged conditions, frequency of depositing events storms, tides , and in that way may allow reconstructions of climate and paleogeographic setting.
Probably the most important sedimentary structures are: In fact, there are thick books whose sole object is to describe and discuss sedimentary structures and their meaning. In a way sedimentary structures are the alphabet in which a lot of earth history is written, and the better we can decipher them the better will our understanding of the geologic past as well as of the future be.
As we can see from above examples , the sedimentary structures that we find in today's sediments are the same that occur in the very oldest sediments known on earth. The implications of this observation of sedimentary structures are twofold: A the surface processes of the earth have been the same throughout earth history, and have been of comparable magnitude.
B because we can examine what processes produce these structures today, we can go back and reconstruct the ancient world. A sedimentary rock that we can examine in an outcrop has a long history and has been subjected to modification by various processes. Rivers are the main transporting agent of material to the oceans glaciers are at times important.
During transport the sediment particles will be sorted according to size and density gold placers and will be rounded by abrasion.
Material that has been dissolved during weathering will be carried away in solution. The sorting during transport is important because it is the reason that we have distinct clastic rock types conglomerates, sandstones, shales. Compaction is effected by the burden of younger sediment that gets piled on top of older sediments rearrangement of particles, packing, dewatering. Minerals precipitated from the pore waters in these sediments cement together adjacent sediment grains.
Thus, a coherent solid rock is formed. Not only oil and gas, but also a large variety of other resources are extracted from sediments and sedimentary rocks. Coal mined extensively in southeastern Indiana and lignite are special kinds of sedimentary rocks carbonaceous sediments; see above , and they constitute a very large resource that should last for several hundred additional years.
Most of the iron ore in the world is mined from Precambrian sedimentary rocks, the largest l ead-zinc-silver and copper deposits occur in sedimentary rocks mostly Precambrian, especially Proterozoic , and the largest gold and uranium deposits also are located in sedimentary rocks as well Archean to Proterozoic in age. Bauxite, the main ore for Aluminum production is basically a fossil soil also a sediment that formed in tropical climates. If we then also add the many building stones that are quarried from sedimentary rocks, and add in the raw materials for ceramics clay minerals from mudstones and shales , it is quite obvious that sedimentary rocks are indeed of considerable importance, and that it pays to understand them well.
Was it famine or scurvy -- I fought it; I hurled my youth into a grave. I wanted the gold, and I got it -- Came out with a fortune last fall, -- Yet somehow life's not what I thought it, And somehow the gold isn't all.
There's the land. Have you seen it? It's the cussedest land that I know, From the big, dizzy mountains that screen it To the deep, deathlike valleys below.
Some say God was tired when He made it; Some say it's a fine land to shun; Maybe; but there's some as would trade it For no land on earth -- and I'm one. You come to get rich damned good reason ; You feel like an exile at first; You hate it like hell for a season, And then you are worse than the worst. It grips you like some kinds of sinning; It twists you from foe to a friend; It seems it's been since the beginning; It seems it will be to the end.
I've stood in some mighty-mouthed hollow That's plumb-full of hush to the brim; I've watched the big, husky sun wallow In crimson and gold, and grow dim, Till the moon set the pearly peaks gleaming, And the stars tumbled out, neck and crop; And I've thought that I surely was dreaming, With the peace o' the world piled on top. The summer -- no sweeter was ever; The sunshiny woods all athrill; The grayling aleap in the river, The bighorn asleep on the hill.
The strong life that never knows harness; The wilds where the caribou call; The freshness, the freedom, the farness -- O God! The winter! The snows that are older than history, The woods where the weird shadows slant; The stillness, the moonlight, the mystery, I've bade 'em good-by -- but I can't.
There's a land where the mountains are nameless, And the rivers all run God knows where; There are lives that are erring and aimless, And deaths that just hang by a hair; There are hardships that nobody reckons; There are valleys unpeopled and still; There's a land -- oh, it beckons and beckons, And I want to go back -- and I will.
They're making my money diminish; I'm sick of the taste of champagne. Thank God! I'll fight -- and you bet it's no sham-fight; It's hell! There's gold, and it's haunting and haunting; It's luring me on as of old; Yet it isn't the gold that I'm wanting So much as just finding the gold.
It's the great, big, broad land 'way up yonder, It's the forests where silence has lease; It's the beauty that thrills me with wonder, It's the stillness that fills me with peace. Metamorphic Rocks. Metamorphic rocks are those whose original texture, composition and mineralogy have been changed by conditions of high pressure and temperature higher than conditions of formation of starting material.
This branch contains quartzite —a metamorphosed form of sandstone —and hornfels. The use of rocks has had a huge impact on the cultural and technological development of the human race. Rocks have been used by humans and other hominids for at least 2. The mining of rocks for their metal ore content has been one of the most important factors of human advancement, which has progressed at different rates in different places in part because of the kind of metals available from the rocks of a region.
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or coal seam. Materials recovered by mining include base metals , precious metals , iron , uranium , coal , diamonds , limestone , oil shale , rock salt and potash. Mining is required to obtain any material that cannot be grown through agricultural processes, or created artificially in a laboratory or factory.
Mining in a wider sense comprises extraction of any resource e. Mining of rock and metals has been done since prehistoric times. Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials and finally reclamation of the land to prepare it for other uses once mining ceases. The nature of mining processes creates a potential negative impact on the environment both during the mining operations and for years after the mine has closed.
This impact has led to most of the world's nations adopting regulations to manage negative effects of mining operations. From Wikipedia, the free encyclopedia. A naturally occurring solid aggregate of one or more minerals or mineraloids.
For other uses, see Rock disambiguation and Stone disambiguation. This article may be expanded with text translated from the corresponding article in Swedish. June Click [show] for important translation instructions. View a machine-translated version of the Swedish article. Machine translation like Deepl or Google Translate is a useful starting point for translations, but translators must revise errors as necessary and confirm that the translation is accurate, rather than simply copy-pasting machine-translated text into the English Wikipedia.
Do not translate text that appears unreliable or low-quality. If possible, verify the text with references provided in the foreign-language article. You must provide copyright attribution in the edit summary accompanying your translation by providing an interlanguage link to the source of your translation. A model attribution edit summary using German: Content in this edit is translated from the existing German Wikipedia article at [[: Exact name of German article]]; see its history for attribution.
For more guidance, see Wikipedia: See also: Formation of rocks. Main article: Igneous rock. Sedimentary rock. Metamorphic rock.
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