Diversity and processes modifying composition of the igneous rocks igneous rock. The core idea is that an original rock, the parent rock, present when the earth formed gave rise not only to all other igneous rocks, but all rocks including sedimentary and metamorphic. Igneous rocks are classified according to their mineral content. The classification for igneous, sedimentary, metamorphic, and pyroclastic rocks is shown on figures 41, 42, 4. Compared to felsic igneous rocks, mafic igneous rocks contain greater amounts of afinegrained and mafic bfinegrained and felsic. 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. Ultramafic rocks are dominated by olivine andor pyroxene. Igneous rocks thus occur in two ways, either as extrusive on the surface rocks or as intrusive below the surface bodies. Viscosity depends on primarily on the composition of the magma, and temperature. A magma consists mostly of liquid rock matter, but may contain crystals of various minerals, and may contain a gas phase that may be dissolved in the liquid or may be present as a separate gas phase. Texture refers to degree of crystallinity, grain size, and geometrical relationships between the cons tituents of a rock fabric. Percent of mineral composition of igneous rocks by chris. Mineral compositions in the deccan igneous rocks of india. Parent material of igneous rocks forms from partial melting of rocks magma at surface is called lava.
This reader emphasizes how all igneous rocks are formed and explores how the formation is related to igneous rock classification. Mount rushmore, where the presidents faces are carved in the mountainside, was chiseled out of granite, another igneous rock. Degassingvolatiles release hydrothermal alteration and lowgrade metamorphism. Half dome is an igneous rock formation in yosemite national park. In addition to texture, igneous rocks may are classified according to their chemical composition. Textures of the igneous rocks structure largescale features recognizable in the field, such as banding, lineation, jointing, and vesicularity. Teacher notes if your students have completed the plate tectonic units on volcanoes, they should be familiar with different volcanic environments. Occurrence, texture, and classification of igneous rocks. Magmas and igneous rocks magma and igneous rocks igneous rocks are formed by crystallization from a liquid, or magma. An extrusive igneous rock with a mineral composition of 35% quartz, 35% potassium feldspar, 15% plagioclase feldspar, 10% biotite, and 5% amphibole is called a basaltic glass b gabbro c granite drhyolite 6.
Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. Because the composition of the crust is generally different from the composition of magmas which must pass through the crust to reach the surface, their is always the possibility that reactions between the crust and the magma could take place. This worksheet utilizes the scheme for igneous rock identification of the esrts and allows students to practice calculating the percentage of each mineral found in a some igneous rocks. The charnockite suite or series is a particularly widespread form of granofels. It is visibly crystalline and usually has a granular texture composed of roughly equally sized crystals although the appearance may vary widely. Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body. A solid that forms from a solution during a chemical reaction in water. Chemical composition of igneous rocks expressed by means of. The felsic minerals include quartz, tridymite, cristobalite, feldspars plagioclase and alkali feldspar, feldspathoids nepheline and leucite, muscovite, and corundum. Intrusive and extrusive igneous rocks are classified based on what criteria. Lab 2 lecture igneous, sedimentary, and metamorphic. Which characteristic of an igneous rock would provide the most information about the environment in which the rock solidi.
Igneous comes from word ignis meaning fire, it is therefore not surprising that igneous rocks are associated with volcanic activity and. The various igneous textures result mainly from the different cooling histories, whereas the mineral composition of an igneous rock is the result of the chemical makeup of the parent magma. Intrusive igneous rocks crystallize below earths surface, and the slow cooling that occurs there allows large crystals to form. The molten rock, or lava, has cooled to form igneous rocks. Most igneous rocks are buried below the surface and covered with sedimentary rock, or are buried beneath the ocean water. Granite composition felsic composition compositional group of igneous rock indicating the rock is composed almost entirely. Rock fragments, highly variable in composition, range from zero to sometimes 80% of rock.
Intermediate composition andesitic composition a compositional group of igneous rocks contain at least 25% dark silicate minerals. Igneous rocks are also geologically important because. Chemical composition of sedimentary rocks in colorado. Finally, students may need their earth science reference tables esrt for parts of the lesson a document used widely in the new york state earth science regents. The major mineralogical components of igneous rocks can be divided into two groups. However, the impact of these compositional variations on chemical weathering, and by extension. Which intrusive igneous rock could be composed of approximately 60% pyroxene, 25% plagioclase feldspar, 10% olivine, and 5% amphibole. Bataille,1 amy willis,2 xiao yang,1 xiaoming liu1 the composition of igneous rocks in the continental crust has changed throughout earthshistory.
Additionally, if you would like all of the resources together in a pdf document, that can be accessed as a complete resource here. Mafic rocks are dominated by plagioclase and pyroxene even if you cant see them with the naked eye and smaller amounts of olivine. Igneous rock is categorized by how it actually formed. Principles of igneous and metamorphic petrology second edition this textbook provides a basic understanding of the formative processes of igneous and metamorphic rocks through quantitative applications of simple physical and chemical principles. The exact location of where the rock forms, determines what type of igneous rock it is. Fragments of any kind igneous, metamorphic or sedimentary rock may occur as rock. Rocks formed from lava are extrusive, or volcanic rocks rocks formed from magma at depth are intrusive, or plutonic rocks. In a general sense, it is the intermediate type between basalt and rhyolite, and ranges from 57 to 63% silicon dioxide sio 2 as illustrated in tas diagrams. Here we give very brief descriptions of most types of terrestrial and lunar igneous rocks, their regional distribution and classification, and examples of their geochemical trends and fingerprints. The classification of the many types of different igneous rocks can provide us with important information about the conditions under which they formed. Igneous rocks are formed from the solidifying of liquid rock material. In practice, this means that the average dimension of the crystals is less than 1 millimeter. Diorite is a plutonic igneous rock with intermediate composition between mafic and felsic rocks.
Naming igneous rocks geologists use both the minerals and texture to classify and name igneous rocks. If crustal rocks are picked up, incorporated into the magma, and dissolved to become part of the magma. Principles of igneous and metamorphic petrology second. How quickly the molten rock cools and crystallizes, and where this occurs with respect to earths surface. I have the honor to transmit herewith a mannsotipt by. Igneous rock, any of various crystalline or glassy rocks formed by the cooling and solidification of molten earth material. A qapf diagram is a double ternary diagram which is used to classify igneous rocks based on mineralogic composition. Igneous rock igneous rock mineralogical components. Classification of igneous rocks mineralogical criteria 1. Because igneous rocks form under diverse conditions, they differ widely in texture, mineral composition, and appearance. Crystallization the formation and growth of a crystalline solid from liquid or gas. Igneous rocks are formed by the cooling and crystallization of molten rock. Igneous rocks result from the final solidification of magma at the surface or at variable depths within the earth, as well as from the eventual consolidation of fragmented debris.
This combination is generated only deep in the crust by tectonic forces that operate on a grand scale, so granofels is a product of regional, rather than contact, metamorphism. Extrusive igneous rocks tend to cool much more rapidly, and the minerals grow quicker and can not get as large. As we know already, igneous rocks form when magma cools and hardens, this can happen underground or on the surface. Igneous rocks and processes revised on 102011 page 5 of 10 finegrained or aphanitic. In describing texture we are generally referring to the average size of the mineral grains present, but other important characteristics include the relative sizes i. Proportion and kinds of ferromagnesium minerals the graniterhyolite family felsic rocks are lightcolored, locally glassy obsidian composed of quartz and potassium feldspar with minor sodium plagioclase, biotite, and amphibole. Model to assess the quality of magmatic rocks for reliable. Igneous rocks that crystallize slowly beneath the earth s surface, typically have visible individual minerals. The book encourages a deeper comprehension of the subject by explaining the.
Chemical composition of sedimentary rocks in colorado, kansas, montana nebraska, north dakota, south dakota, and wyoming compiled by thelma p. Granofels are one of the few nonfoliated rocks to form under relatively high temperatures and pressures. On the other hand, if a magma is iugs classification of igneous rocks with respect to silica, then og silica mineral should not precipitate from the magma, and iugs classification of igneous rocks should not be present in the rock. A brief discussion of the major rock groups igneous, sedimentaryand metamorphic, and their most common forms is also included. In some places, geological processes have brought igneous rocks to the surface. Get a printable copy pdf file of the complete article 627k, or click on a page image below to browse page by page. Igneous rocks pictures of intrusive and extrusive rock types. Scientists have found it useful to describe the chemical composition of magma, as well as any volcanic rock that is derived from magma, in terms of the weight. A study of geochemistry through the use of standardised graphs. The texture of a rock is a result of various processes.
Pdf mineral compositions in the deccan igneous rocks of. Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Lava is molten rock flowing out of fissures or vents at volcanic centers when cooled they form rocks such as basalt, rhyolite, or obsidian. Full text full text is available as a scanned copy of the original print version. Extrusive igneous rocks tend to cool much more rapidly, and the minerals grow quicker and can not.