The minerals that make up igneous rocks crystallize at various different temperatures. Plutonic bodies can be tabular, cylindrical or somewhere between equidimensional and irregular. Igneous rock is formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planets mantle or crust.
Basalt is the most common extrusive volcanic igneous rock. Pdf petrogenesis of the mafic igneous rocks of the betic. Light colored igneous rocks, those dominated by nonferromagnesian silicates silicates are called felsic igneous rocks and are either pink or light gray. Through various parts of the spreading process, permeability can be generated in both the intrusive gabbros and extrusive basalts. Student materials for this exercise include an instructionquestion file, a microsoft excel spreadsheet with with data for various types of igneous rocks, and an image file illustrating rock samples pdf. Rocks formed from lava are extrusive, or volcanic rocks. Stratigraphic sequence of layering in the eastern lobe of the bushveld complex. The minerals found in these types of deposits and the deposit. Typical occurrences of igneous rock bodies on the surface include lava flows, lava domes, necks and spines. The composition of an igneous rock is described on the basis of the minerals present. Ore deposits related to mafic igneous rocks range from largest, most extensive igneous petrologic systems in the world e.
Mostly k spar no quartz syenite pegmatitic mostly feldspar. Igneous rocks are formed when magma cools, either on earths surface or beneath it, though some may form by fragmentation of solidifying magma. The resulting geothermobarometers involve thermodynamic expressions that relate temperature and pressure to. The minerals found in these types of deposits and the deposit types themselves are described and discussed individually, mineral resource tracts and. An introduction to igneous rocks for the beginner a very simple igneous classification pdf version for printing alphabetical listing of igneous rocks links to picturesdescriptions bowens reaction series and igneous rock forming minerals pdf version magma types ultramafic, mafic, intermediate, felsic strategies of igneous rock classification. A new upb chronometer for mafic igneous rocks precise dates for mafic igneous events are essential for tectonic reconstructions and understanding mantle dynamics, mass. Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the earth magma is a mixture of liquid rock, crystals, and gas. Coarsegrained intermediate igneous rocks are said to have a salt and pepper appearance.
A dark mafic, dense, igneous rock with a fine texture, found in oceanic crust diorite coarsegrained igneous rock of intermediate composition equal black and white. Metamorphism of mafic rocks mineral changes and associations along t p gradients characteristic of the three facies series hydration of original mafic minerals generally required if water unavailable, mafic igneous rocks will remain largely unaffected, even as associated sediments are completely re. Basalt is finegrained, whereas gabbro is coarsegrained. Igneous rocks and processes revised on 102011 page 3 of 10 reaction series contains all of the common ironforming ferromagnesian minerals. Classification of igneous rocks geosciences libretexts. Kimberlites are product of continental interpolate magmatism and confined to regions underlain by old cratons economic kimberlites occur only on archon cratons primary deposit. Ultramafic rocks also referred to as ultrabasic rocks, although the terms are not wholly equivalent are igneous and meta igneous rocks with a very low silica content less than 45%, generally 18% mgo, high feo, low potassium, and are composed of usually greater than 90% mafic minerals dark colored, high magnesium and iron content. Igneous rock igneous rock mineralogical components. The lower part of oceanic crust is comprised of gabbro. How to classify igneous rocks into ultramafic, mafic. Chapter 4 magmas, igneous rocks, and intrusive activity.
Pdf mafic igneous rocks are widespread in the nevadofilabride complex, the lowermost metamorphic unit of the internal zones of the betic cordilleras. Felsic is a term that is used to refer to igneous rocks rich in mineral feldspar. They include two types volcanic or extrusive igneous rocks form when the magma cools and crystallizes on the surface of the earth. Irelandd, and weidong suna,b,c,1 acenter of deepsea research, institute of oceanology, chinese academy of sciences, 266071 qingdao, china. The whole complex lies discordantly in precam brian gneissic terrane and is overlain by tertiary volcanic rocks. Texture refers to the size and arrangement of crystals, glass and pyroclasic material in a rock. Magma, and the igneous rock it becomes, has a range of chemical compositions. The broad compositional classes are felsic for rocks that are dominated by nonferromagnesian minerals and mafic for rocks that are dominated by ferromagnesian minerals. The classification is done based on their silica content, as silica is usually the most abundant of all the oxides present. Pdf thermobarometry of mafic igneous rocks based on. Ore deposits of mafic igneous rocks geology papers. Physical geology in our overview of the earth, we found out that earths internal heat combined with other mechanisms causes rocks to melt in the asthenosphere and lithosphere.
Teacher notes if your students have completed the plate tectonic units on volcanoes, they should be familiar with different volcanic environments. Intermediate gradations amphibolite rock with relict igneous textures and mineralsalso occur. Igneous rocks of broadly basaltic composition are widely distributed in the anorthositebearing. Igneous rocks consist of primarily 12 types of oxides. This reader emphasizes how all igneous rocks are formed and explores how the formation is related to igneous rock classification. They include two types zvolcanic or extrusive igneous rocks form when the magma cools and crystallizes on the surface of the earth zintrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the earth. The nomenclature for these classifications necessitates only 297 rock. Models for estimating the pressure and temperature of igneous rocks from coexisting clinopyroxene and liquid compositions are calibrated from existing data and from new data obtained from experiments performed on several mafic bulk compositions from 830 kbar and 11001475 c. For example, basalt is a mafic lava flow rock which originates from melting of the upper mantle. Mafic rock, in geology, igneous rock that is dominated by the silicates pyroxene, amphibole, olivine, and mica. Thermobarometry of mafic igneous rocks based on clinopyroxeneliquid equilibria, 030 kbar article pdf available in contributions to mineralogy and petrology 1231. The minerals found in these types of deposits and the deposit types themselves are described and discussed individually, mineral resource tracts and areas of interest are. Ternary classification of felsic to mafic igneous rocks.
The composition of the original magma determines how far the reaction process can. The top diagram is for extrusive rocks and the lower is for intrusive rocks. Igneous textures the texture of a rock is a result of various processes that controlled the rock s genesis and, along with mineralogy and chemical composition, provides information that we may use to interpret the rock s origin and history table 3. Mafic rocks that constitute the igneous oceanic crust are created at midocean ridge seafloor spreading centers as a byproduct of partial melt from upwelling mantle. Igneous rocks that crystallize slowly beneath the earth s surface, typically have visible individual minerals. Formed through interaction, mixing, and recycling through the rock cycle. Mineral grains are easily visible to the unaided eye, plutonic, and cool very slowly. Metamorphism of mafic rocks l clinopyroxene breaks down to a number of mafic minerals, depending on grade. Magnesium and iron rich, silica poor, dark rock such as gabbro and basalt. They are known as intrusive or plutonic igneous rocks.
The major mineralogical components of igneous rocks can be divided into two groups. Igneous petrology igneous rocks are assemblages of minerals predominantly rockforming minerals. Intermediate igneous rocks tend to have intermediate shades or colors green, gray, brown. Igneous rocks types, classification, properties, formation. These minerals are high in magnesium and ferric oxides, and their presence gives mafic rock its characteristic dark colour. Igneous rocks form as molten rock cools and solidifies general characteristics of magma. For each area describe the igneous rocks and rock cycle processes you would expect to be occurring at these areas. Magma rises as a result of its low density compared to surrounding rocks. First determine composition, which is based on mineral content or color, if you cant see minerals. All igneous rocks that form from the slow cooling of magma are collectively called plutonic.
These groups refer to differing amounts of silica, iron, and magnesium found in the minerals that make up the rocks. Magmas and igneous rocks magma and igneous rocks igneous rocks are formed by crystallization from a liquid, or magma. Extrusive igneous rocks tend to cool much more rapidly, and the minerals grow quicker and can not get as large. Based on the color andor mineral composition, classify your 9 igneous rock samples r1 through r9 as mafic, felsic, or intermediate. For igneous rock, the composition is divided into four groups.
If the mineral mode cannot be determined as is often the case for volcanic rocks, then a chemical classification of total alkalis versus silica tas is used. The three minerals at the bottom do not form by reaction with the firstformed crystals. The petrology and geochemistry of mafic igneous rocks in the. Most of these rocks are gray though mafic rocks are also found in brown, green, and even black colors. Global atmospheric oxygen variations recorded by thu systematics of igneous rocks he liua,b,c, robert e. Occurrence, texture, and classification of igneous rocks. Typically, the melting is caused by one or more of. Mafic rocks often also contain calciumrich varieties of. At convergent plate boundaries drawing or definition part of the ocean lithosphere created at divergent plate boundaries descends into the earth again, where it heats up and fractionally melts drawing. Is a critical step in the development of a crystal. The resulting geothermobarometers involve thermodynamic expressions that relate temperature and. Therefore, rocks are divided into ultramafic, mafic, intermediate, and felsic. The felsic minerals include quartz, tridymite, cristobalite, feldspars plagioclase and alkali feldspar, feldspathoids nepheline and leucite, muscovite, and corundum.
Igneous rocks and processes revised on 102011 page 5 of 10 finegrained or aphanitic. Mafic rock is commonly contrasted with felsic rock, in which. Iron and, to a lessor extent, magnesium give minerals a darker color. The identification and classification of an igneous rock is typically a two fold process that requires the determination of the type of cooling unit that the rock sample was taken from in the field and an estimation of its mineralogical and chemical composition. In practice, this means that the average dimension of the crystals is less than 1 millimeter. Parent material of igneous rocks forms from partial melting of rocks magma at surface is called lava general characteristics of magma general characteristics of magma. Igneous rocks can evolve from or into metamorphic and sedimentary rocks. Silica content in mafic rocks is around 50% by weight.
Composition refers to a rock s chemical and mineral makeup. The classification and nomenclature of igneous rocks are treated in the final section. Igneous rocks are classified based on composition, from ultra mafic silica poor and iron rich to felsic silica rich and iron poor. Also, basalt is the name given to a finegrained extrusive igneous rock with a mafic composition but the intrusive equivalent is called gabbro fig. Igneous rocks aphanitic andor vesicular pegmatitic or phaneritic glassy pyroclastic mostly feldspar minerals mostly mafic minerals mostly k spar mostly plagioclase 4585% mafic 85100% mafic quartz no quartz felsic. Mafic is an adjective describing a silicate mineral or igneous rock that is rich in magnesium and iron, and is thus a portmanteau of magnesium and ferric. Common mafic rocks include basalt, diabase and gabbro. Igneous rock compositions igneous rocks are composed of silicate minerals for describing ingenious rocks we separate the silicate minerals into two groups. Igneous rocks are formed by crystallization from a liquid, or magma.
Plagioclase makes up the continuous reaction series. The way that magma turns into a solid rock gives it a distinctive igneous texture. Most mafic minerals are dark in color, and common rockforming mafic minerals include olivine, pyroxene, amphibole, and biotite. Hydrothermal activity spatially associated with ultramafic rocks, usually serpentinites, has been observed at several localities proximal. Dark or ferromagnesian silicate minerals have the dominant cations. Igneous rock identification university of washington.
Note that differences in color are not always due to differences in composition, so even in. Mineral deposits related to mafic igneous rocks include podiform chromite, ultramafichosted talcmagnesite, and serpentinehosted asbestos. Ore deposits related to mafic igneous geology papers. Rocks with mafic content 90% have their own classification. In the process the parent rock of the earths interior fractionates to form mafic igneous rocks, e. The iugs systematics of igneous rocks journal of the.
The color distinction comes from the differences in iron and magnesium content. Global atmospheric oxygen variations recorded by thu. Apr, 2018 well that somewhat depends on what kind of igneous rock we are talking about. Igneous rocks are classified on the basis of their composition and their texture. Main zone the thickest zone and contains thick monotonous sequences of hypersthene gabbro, norite, and anorthosite figure 126. Note that rocks with glassy or pyroclastic textures may be described by the above compositions, but that for these specimens the final rock name must still. Igneous rock derived from the latin word ignis meaning fire, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Intrusive or plutonic igneous rocks wherein the magma crystallizes at depth in the earth. Most mafic minerals are dark in color, and common rock forming mafic minerals include olivine, pyroxene, amphibole, and biotite. An igneous rock or a part of an igneous rock with a finegrained or aphanitic texture has crystals, but they are too small to recognized with the unaided eye. If,in the initially stages of such mixing, the magma were erupted, then we might expect to find rocks that show a marble cake appearance, with dark colored mafic rock intermingled with lighter colored rhyolitic rock. Extrusive mafic igneous rocks, basalts and andesites. The most common examples of rocks classified as mafic are gabbro, dolerite, and basalt. Plutonic rocks are always intruded into preexisting sedimentary.
Page 1 lab 3 identification of igneous rocks introduction. Igneous rocks are classified by texture and composition both are used. Thermobarometry of mafic igneous rocks based on clinopyroxene. Lecture notes 3 igneous rocks glendale community college. Classifying igneous rocks mafic 4552% silica igneous rocks are dark colored because they are largely composed of caplagioclase and pyroxene. Part i introduces the concept of composition for igneous rocks. Difference between mafic and felsic compare the difference. Very tiny initial crystals have a high ratio of surface area to volume, and thus, a large proportion of ions at the surface however, surface ions have unbalanced charges because lack the complete surrounding lattice. Mafic rocks tend to be dark in color black, very dark brown, very dark gray, dark green mixed with black.
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