Rocks

Rocks

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  RocksRocks Rocks are dividedby origin into three types: 1. Igneous Rocks: are formed from the solidification of molten rock material. whether crystallized on the surface and below the surface or in the ground. Arock is a naturally formed, consolidated material usually composed of grains of one or more minerals. Petrology: Which is interested in studying rocks, origin, composition and physical properties and the nature of the changes taking place due to the different geological processes. rocks and minerals Considered of the main components of the earth's crust. 1
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  2. Sedimentary Rocks:are the secondary rocks which are formed from the loose fragments or clastic sediments produced by weathering of older rocks. 3.Metamorphic Rocks: which are formed from other rocks by Metamorphism process due to the effects of High temperature, High pressure and Chemical fluids 2
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  Rock Cycle innature The rock cycle shows how one type of rocky material gets transformed into another • Magma is created by melting of rock above a subduction zone • Less dense magma rises and cools to form igneous rock • Igneous rock exposed at surface gets weathered into sediment • Sediments transported to low areas, buried and pressured into sedimentary rock • Sedimentary rock heated and pressured at depth to form metamorphic rock • Metamorphic rock may heat up and melt at depth to form magma 3
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  • Igneous rocksare formed from two basic types: Formation of Igneous Rocks Intrusive or Plutonic rocks: Intrusive rocks form when magma solidifies underground and the slow cooling to form large crystals, it is known as gragunal texture. Examples of intrusive igneous rocks are granite , diorite, gabbro, and peridotite. Extrusive or Volcanic rocks: Extrusive rocks form when magma solidifies at the Earth’s surface (lava) where they cool quickly to form small crystals, it is known as Aphanitic texture. These rocks include rhyolite , andesite, basalt , dacite. Some cool so quickly that they form glass texture such as obsidian, pumice 1- Igneous Rocks1- Igneous Rocks • Magma is molten rock. 5
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  • Intrusive rocksexist in bodies or structures that penetrate or cut through pre-existing country rock • Intrusive or Plutonic bodies are given names based on their size, shape, depth and relationship to country rock – Shallow intrusions: Dikes and sills FORMS OF INTRUSIVE IGNEOUS ROCKS Dikes: Dikes are relatively thick tabular sheetlike body that penetrates virtically to the bedding planes. Mafic dyke 6
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  SILLS: Sills arerelatively thin tabular sheetlike body that penetrates parallel to the bedding planes. • They are discordant • Cut across the bedding of the rocks in which they intrude • Thickness vary widely from an inch upto hundred of feet • Injected through fractures, joints, and weak planes 7
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  Depth intrusions: Laccolith,Phacolith, Lopolith, Batholith Laccolith: It is a concordant body, with flat bottom and convex upward. It is dome shaped Phacolith: These are concordant bodies that occurs along the crests and troughs of the folded sedimentary strata. 8
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  Batholith: are thelargest kind of plutons, irregular in shape and occupies large area. Stocks: Are smaller irregular bodies with 10 km in maximum dimension, and are associated with batholiths. Lopolith: These are basin or saucer-shaped concordant bodies with top nearly flat and convex bottom. 9
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  10 Extrusive rocks: volcanic rocksare in the form of large lamellar bodies produced from the flow of magma on the earth surface and be irregular in shape and called by lava: may be 1. scoria: the upper surface of the lava filled by the gaps as a result of the escape of gases. 2.Ropy: Contains long protrusions and curved- like mountains. 3. Blocky: The blocks are irregularly shaped
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  Classification of IgneousRocksClassification of Igneous Rocks 1- Mode of formation: Volcanic and PlutonicVolcanic and Plutonic 2- Texture of rocks: Textural classified into: – Plutonic rocks (gabbro-diorite-granite) are coarse- grained and cooled slowly at depth – Volcanic rocks (basalt-andesite-rhyolite) are typically fine-grained and cooled rapidly at the Earth’s surface 11
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  3- Mineralogical Composition:are divided into: 1. Major minerals include sillicate minerals: - Acidic rocks composed of silica and aluminum bearing minerals and light-colored (e.g. quartz, orthoclace, plagioclace and muscovite ). -Basic rocks composed of magnesium and iron bearing minerals and dark-colored (e.g. biotite, pyroxene, hornblend and olivine). 2. Secondary minerals: 12
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  • 4- ChemicalComposition: particularly silica (SiO2) content, determines mineral content and general color of igneous rocks – Felsic (silicic) rocks have >65% silica, by weight, and contain light-colored minerals that are abundant in silica, aluminum, sodium and potassium • Intrusive/extrusive felsic rocks - granite/rhyolite – Intermediate rocks have 65-52% silica, by weight • Intrusive/extrusive intermediate rocks - diorite/andesite 13
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  – Mafic rockshave 52-40% silica, by weight, and contain dark-colored minerals that are abundant in iron, magnesium and calcium • Intrusive/extrusive mafic rocks- gabbro/basalt – Ultramafic rocks have <40% silica, by weight, and are composed almost entirely of dark- colored ferromagnesian minerals • Most common ultramafic rock is peridotite (intrusive) 14
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  Granite is  a  coarse-grained,  light colored,  intrusive  igneous  rock  that  contains  mainly quartz,  feldspar,  and  mica minerals.  Rhyolite is  a  light-colored,  fine-grained, extrusive igneous  rock  that  typically  contains  quartz and feldspar minerals.  16
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  Diorite is a coarse-grained,  intrusive igneous rock that  contains a mixture of feldspar,  pyroxene, hornblende and  sometimes quartz.  Andesite is  a  fine- grained, extrusive igneous  rock composed  mainly  of plagioclase (anorthite),  hornblende and biotite.  17
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  Basalt is  a  fine-grained, dark- colored  extrusive  igneous  rock  composed  mainly  of plagioclase and pyroxene.  Gabbro is  a  coarse-grained,  dark  colored,  intrusive  igneous  rock  that  contains  feldspar,  pyroxene  and  sometimes olivine.  18
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  Peridotite is  a  coarse-grained intrusive  igneous  rock  that  is  composed  almost  entirely  of olivine.  It  may  contain small amounts of amphibole, feldspar, quartz or  pyroxene.  19