Petrology - Igneous Rocks PDF

PETROLOGY  ▪Definition of Terms ▪Classifications of Rocks TOPICS ▪Origin and Occurrence of Rocks ▪Engineering Importance of Rocks Definition of Terms  PETROLOGY - the branch of geology that deals with formation of rocks, their clas...

PETROLOGY  ▪Definition of Terms ▪Classifications of Rocks TOPICS ▪Origin and Occurrence of Rocks ▪Engineering Importance of Rocks Definition of Terms  PETROLOGY - the branch of geology that deals with formation of rocks, their classification and occurrence ROCK - naturally occurring solid aggregates or masses of minerals, mineraloids, or organic material that make up the Earth’s crust. https://museum.wales/curatorial/natural-sciences/petrology/ MINERAL - a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties. MINERALOID - a naturally occurring, inorganic solid that does not exhibit crystallinity. It may have the outward appearance of a mineral, but it does not have the "ordered atomic structure" required to meet the definition of a mineral. Some mineraloids also lack the "definite chemical composition" required to be a mineral. Organic material - anything that was alive and is now in or on the soil. Classifications of Rocks https://www.sciencefacts.net/igneous-rocks.html https://longacresranch.org/petrology-science-rocks/ https://www.sciencefacts.net/sedimentary-rocks.html https://www.sciencefacts.net/metamorphic-rocks.html https://longacresranch.org/petrology-science-rocks/ Origin of Igneous Rocks Igneous rocks are formed when molten material from within the Earth, called magma, cools down and solidifies forming crystals. Igneous rocks are characterized by an interlocking crystalline texture. https://geologyglasgow.org.uk/minerals-rocks-fossils/igneous-rocks/ https://makeagif.com/gif/igneous-rocks-CFBfY8 https://grade8science.com/5-1-1how-do-rocks-form/ Intrusive Extrusive Classifications of Igneous Rocks Based on Mode of Occurrence Intrusive Igneous Rocks - formed by the crystallization of the magma within the Earth’s crust Extrusive Igneous Rocks - formed by the crystallization of the magma as it exits as lava and cools above (or very near) the Earth's surface. Classifications of Igneous Rocks Based on Mode of Occurrence Intrusive Igneous Rocks - formed by the crystallization of the magma within the Earth’s crust Intrusive Rock Type Depth inside the Earth Rate of Cooling Texture Examples Coarse Granite Plutonic 7 – 10 km Very slow grained Syenite greater than 5 mm Gabbro in diameter) Medium Microgranite Hypabyssal grained Up to 2 km Slow Porphyry (Sub-volcanic) between 5 to 1 mm Dolerite in diameter Plutonic Rocks Examples Granite Syenite https://rocksminerals.flexiblelearning.auckland.ac.nz/rocks/syenite.html https://www.geologypage.com/2019/05/granite-rocks.html Gabbro https://rocksminerals.flexiblelearning.auckland.ac.nz/rocks/syenite.html Hypabyssal Rocks Examples Porphyry Microgranite https://www.sandatlas.org/porphyry/ https://www.geologypage.com/2019/05/granite-rocks.html Dolerite https://rockidentifier.com/wiki/Dolerite.html  Processes that expose intrusive rocks on the Earth’s surface DENUDATION – erosion of the overlying strata and therefore uplifting the underlying ones. TECTONIC ACTIVITY – movement of the Earth’s tectonic plates https://investingnews.com/daily/resource-investing/base-metals-investing/copper-investing/copper-porphyry-takeover-target/ Classifications of Igneous Rocks Based on Mode of Occurrence Extrusive Igneous Rocks - formed by the crystallization of the magma as it exits as lava and cools above (or very near) the Earth's surface. Intrusive Rock Type Location Rate of Cooling Texture Examples Fine Obsidian On the Earth’s grained Volcanic Very fast Pumice surface Less than 1 mm in Rhyolite diameter) Volcanic Rocks Examples Rhyolite Obsidian https://www.amazon.com/Raw-Rhyolite-Igneous-Rock-Specimen/dp/B083T9DZ28 http://geologylearn.blogspot.com/2015/03/obsidian.html Pumice https://geologylearn.blogspot.com/2015/03/pumice.html Classifications of Igneous Rocks Based on Chemical Composition Intrusive Rock Silica content Major mineral content Color Type Quartz Felsic (Acidic) > 66 % Alkali feldspar Light Biotite Intermediate 55 – 66 % Alkali feldspar Light to gray Hornblende Magnesium Mafic (Basic) 45 – 55 % Iron Black Plagioclase feldspar Pyroxene Olivine Ultrabasic < 45 % Magnesium Black to Olive green Iron Examples of Felsic (Acidic) Rocks Microgranite https://www.virtualmicroscope.org/content/riebeckite-microgranite Granite Syenite https://www.igscountertops.com/countertop-glossary/ https://geologyscience.com/rocks/igneous-rocks/syenite/ Examples of Felsic (Acidic) Rocks Rhyolite https://geology.com/rocks/pictures/rhyolite-specimens.jpg Examples of Intermediate Rocks Diorite https://www.sciencephoto.com/media/1148500/view/diorite Monzonite Andesite https://www.gemrockauctions.com/learn/a-z-of-gemstones/andesite https://www.sandatlas.org/monzonite/ Examples of Mafic Rocks Diabase https://www.sandatlas.org/diabase/ Basalt Gabbro https://rocksminerals.flexiblelearning.auckland.ac.nz/rocks/gabbro.html https://https://www.sandatlas.org/basalt/.sandatlas.org/basalt/ Examples of Ultramafic Rocks Komatiite https://www.alexstrekeisen.it/english/vulc/komatiites.php Harzburgite Kimberlite https://www.mindat.org/min-48035.html https://www.science.smith.edu/~jbrady/petrology/rock-library/igp-rocks/harzburgite/harzburgite.php Microgranite Andesite Basalt Kimberlite  Nepheline Pegmatite Gray is nepheline Yellowish brown is wöhlerite Black is hornblende Pink is K-feldspar Gray is magnetite https://www.alexstrekeisen.it/english/pluto/nephelinepegmatite.php  Syenite Pink alkali feldspar Dark green aegirine-augite White lamellae https://geologyistheway.com/igneous/syenite/ Classifications of Igneous Rocks Based on Texture Texture Rate of Cooling Crystal Size Large crystals Phanerites Slow cooling generally ½ mm to 5 mm Small crystals Aphanites Rapid cooling generally less than ½ mm Glassy (Vitreous) Very fast zero grain size https://www.geologyin.com/2014/09/what-is-difference-between-phaneritic.html Examples of Glassy Rocks Pitchstone https://geology.cochise.edu/igneous-rock/pitchstone-3/ Obsidian Scoria https://rockseeker.com/different-types-of-obsidian/ https://www.britannica.com/science/scoria Classifications of Igneous Rocks Based on Color Index Rock Division Color Index, M Leucocratic 0 - 15 Felsic (Acidic) Mesocratic 16 - 45 Intermediate Melanocratic 46 - 85 Mafic (Basic) Hypermelanic > 85 Ultrabasic Color Index, M - a number that represents the percent, by volume, of dark-colored (i.e., mafic) minerals in a rock. - the percentage of mafic minerals M minus the content of apatite, carbonates, muscovite, zircon, etc. https://www.mindat.org/glossary/color_index  Igneous Rock Classification Chart https://www.facebook.com/photo/?fbid=695728437751792&set=a.182396909084950 Examples of Rocks with Different Color Indices Melanocratic alkalifelspar-granite-with-turmaline_13800.html https://www.topgeo.com/leucocratic-mu-bi- Gabbro Mesocratic Lamprophyre Leucocratic Granite https://geology.com/rocks/peridotite.shtml https://www.topgeo.com/leucocratic-mu-bi-alkalifelspar-granite- with-turmaline_13800.html https://www.topgeo.com/leucocratic-mu-bi- alkalifelspar-granite-with- turmaline_13800.html Hypermelanic Peridotite Engineering Importance of Rocks Importance of Igneous Rocks The igneous rocks are typically impervious, hard and strong and form very strong foundations for most of civil engineering projects such as dams and reservoirs. Many of the igneous rocks are used extensively as materials for construction. Granites, syenites and dolerites possess very high crushing strength and are therefore supposed to be most suitable for construction works. Although, basalts and other dark coloured igneous rocks are equally strong, these are recommended for use in foundation of structures and roads only. Until traversed by joints, these rocks are the best for tunnels. Some of the igneous rocks like peridotites and pegmatites are very valuable; they may contain many valuable minerals of much economic worth. Moreover, their minerals and chemistry give information about the composition of the mantle, from which some igneous rocks are extracted, and the temperature and pressure conditions that allowed this formation, and/or of other pre-existing rock that melted. Examples of Igneous Rocks and Their Characteristics and Uses Granite - plutonic acidic igneous rock Mineralogical Composition Granite is mainly composed of quartz and feldspar with biotite and hornblend. The colour of different granites is derived by the presence of feldspar, i.e. albite and orthoclase. Microcline and tourmaline may also be present as an accessory mineral. Texture The texture of granite depends upon the mineral composition as well as their mutual relationship. Granite shows porphyritic as well as intergrowth texture, depending upon the abundance of quartz to feldspar. Occurrence Granites generally occur in the crust of the Earth and one of the most abundant igneous rock. They are mainly situated as deep-seated intrusive bodies like sills, and batholiths. Granites are exposed on the surface as an outcrop after erosion activities. Use Granites are widely used in building materials as decorative stones, both as exterior and interiors. Different types of granites are also used for geological studies. Diorite - intermediate and plutonic igneous rock Mineralogical Composition Diorites are typically rich in feldspar plagioclase of sodic group (e.g. albite). Besides plagioclase and alkali feldspars, diorites also contain accessory minerals like hornblende, biotite and some pyroxenes. Quartz is uncommon in diorite; but sometimes if it is present, it would be called as quartz-diorite. Texture The texture generally observed in diorite varies from coarse- to medium-grained and has holocrystalline arrangement of different mineral grains. It shows ineguigranular texture, particularly panidiomorphic textur. Occurrence Diorite commonly occurs as small intrusive bodies like dikes, sills, stocks and other irregular intrusive masses. They also get formed at the margins of bigger igneous masses called igneous pluton. It is found as hypabyssal rock. Use Diorite is used in buildings as decorative stones and also as aggregate. Andesite - volcanic igneous rock Mineralogical Composition It is constituted by plagioclase. Andesite may contain small amounts of quartz as well as biotite, hornblende, augite, olivine and hypersthene from the dark minerals giving them an overall greyish or darker appearance. Texture The texture generally observed in diorite varies from coarse- to medium-grained and has holocrystalline arrangement of different mineral grains. It shows ineguigranular texture, particularly panidiomorphic texture. Occurrence Andesite occurs abundantly as volcanic rocks, next to basalts, and may also occur as crystallized lava flows of extensive dimensions. Use Polished blocks of andesite make it eminently suitable as a decorative building stone. Andesite is used in buildings as decorative stones and in the paint industry. Syenite - plutonic coarse-grained, intermediate type of rock Mineralogical Composition Syenites mainly contain feldspars of which many types may occur simultaneously in the same rock or in different varieties. The most common feldspars of syenite are orthoclase and albite. Microcline, oligoclase and anorthite are also present in them as accessory minerals. In some syenites, the minerals like nepheline, and leucite are present. Common accessory minerals occurring in syenites are apatite, zircon, and sphene. Quartz is absent and rarely present as a minor accessory. Texture Syenite shows textures coarse- to medium-grained textures, holocrystalline in nature and exhibit graphic, inter-grown or porphyritic relationship among its constituents. Occurrence Syenite occurs in the plutonic stage of igneous activity when a suitable composition of magma is cooled down. Use Syenite is used in buildings as decorative stones and also in the extraction of nephaline as mineral. Gabbro - plutonic basic rock Mineralogical Composition Plagioclase feldspars of lime and soda composition (e.g. labradorite and anorthite) are the chief constituents of gabbro. Besides these, the mafic minerals like augite, hornblende, olivine, biotite and iron oxides are common as accessory minerals. Texture Gabbro shows inequigranular textures in which augite or olivine mineral encloses the plagioclase. The modal abundance of plagioclase is more than augite or olivine. Reaction rim is also well observed in gabbro. Occurrence Gabbro occurs under plutonic condition and is associated with convergent plate margin. Use Gabbro is used in buildings as decorative stones and also in the extraction of plasioclase as mineral. Dolerite - volcanic basic rock of typically hypabyssal origin Mineralogical Composition Dolerite is predominantly made up of calcic plagioclase (e.g. anorthite and labradorite). Dark minerals like augite, olivine and iron oxide, etc., are also present in good proportions along with the plagioclase minerals. Texture Ophitic texture is very common in which augite mineral encloses the plasoclase. Occurrence Sills and dykes of doleritic composition have been recorded at many places associated with magmatic activity. Use Dolerite is used in buildings as decorative stones and in the extraction of plasioclase as mineral. Basalt - volcanic basic rock Mineralogical Composition Basalts are commonly made up of calcic plagioclase feldspars (anorthite and labradorite) and a number of ferro-magnesian minerals like augite, hornblende, hypersthene, olivine, biotite and iron oxides, etc. In fact, many types of basalts are distinguished on the basis of the type and proportion of ferro-magnesian minerals in them. Occurrence Basaltic rocks form extensive lava flows on the continents and also on the oceanic floors at divergent and convergent boundaries in almost all the regions of the world. Use Basalt is used in buildings as decorative stones and in the extraction of zeolite as mineral. Pegmatite - an exceptionally coarse grained igneous rock formed from hydrothermal solutions emanating from magmas that get cooled and crystallized in cavities and cracks around magmatic intrusions. Mineralogical Composition Pegmatites exhibit great variation in their mineral composition. The granite pegmatites contain alkali feldspars (like orthoclase and microcline) and quartz as the dominant minerals. A variety of other minerals like tourmaline, micas (muscovite and biotite), topaz, fluorite, spodumene, beryl, cassiterite, wolframite, columbite and tantalite, etc., occur in different pegmatites. Texture Pegmatites do not show any special textures and structures, except that they are invariably coarse grained and mostly inequigranular. Occurrence Pegmatite occurs in fissures and cracks in existing igneous and metamorphic rocks as a later phase of magma crystallizes and solidified in cracks. Use These rocks are used for their containing big-sized crystals of minerals. Some of these crystals may be gems and other precious minerals. Lamprophyre - typically occur as dykes and sills. Mineralogical Composition Mostly they are rich in ferro-magnesian silicates. Important minerals forming lamprophyres are biotite, augite and other pyroxenes, hornblende and other amphiboles, feldspars and olivine. Texture Lamprophyre are invariably coarse grained and mostly inequigranular. Occurrence Lamprophyres occur in fissures and cracks in existing igneous and metamorphic rocks as the later phase of magma crystallizes and gets solidified in cracks. Use These rocks are used for their containing big-sized crystals of minerals. Some of these crystals may be gems and other precious minerals. Peridotite - an ultra-mafic, coarse grained, plutonic igneous rocks. Mineralogical Composition It is highly rich in a ferro-magnesian mineral like olivine and augite, which has a composition of (Mg,Fe)SiO4· This is characterized by a low silica index; (when silica is less than 45%). Texture Peridotites are generally massive and coarse grained in texture. Occurrence Peridotites occur in form of sills and dykes of moderate size and are found at deeper depth. Use Peridotites are not common igneous rocks, but it is a suitable rock to replace the basalt and dolerite for giving dark appearance in building exteriors. The olivine and augite minerals are also extracted from this rock. https://www.nps.gov/places/sunrise-road-columnar-rock-formation.htm