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Rock Cycle & Igneous Rocks Chapter 5 Minerals vs. Rocks • Minerals are made of elements • Rocks are a solid substance made up of one or more minerals. Rock Cycle- the continuous movement from one type of rock to another 3 Types of Rocks 1. Igneous Rocks : Formed from the cooling of molten rock. (Granite, Basalt) 2. Sedimentary Rocks : 3. Metamorphic Rocks : 3 Types of Rocks 1. Igneous Rocks : Formed from the cooling of molten rock. (Granite, Basalt) 2. Sedimentary Rocks : Formed in layers as the result of moderate pressure on accumulated sediments.(small rocks compacted together, limestone) (cementation, compaction) 3. Metamorphic Rocks 3 Types of Rocks 1. Igneous Rocks : Formed from the cooling of molten rock. (Granite, Basalt) 2. Sedimentary Rocks : Formed in layers as the result of moderate pressure on accumulated sediments.(small rocks compacted together, limestone) (cementation, compaction) 3. Metamorphic Rocks : Formed from older "parent" rock (either igneous or sedimentary) under intense “heat and pressure” at considerable depths beneath the earth's surface. (ex. limestone becomes marble) The Rock Cycle The interrelationship among the rock types is called … THE ROCK CYCLE. Basically a “recycling machine” of rocks. http://science.cc.uwf.edu/sh/curr/rockcyc/rockcyc.htm Lithification-The physical and chemical processes that turn sediment into sedimentary rock Cementation- occurs when mineral growth chemically glues sediment grains together into solid rock. Stop here Show Rock Cycle Videos http://www.schooltube.com/video/503ca20 5aae459f47494/The-Rock-Cycle http://youtu.be/pm6cCg_Do6k Interactive Animation http://www.bbc.co.uk/bitesize/ks3/science/e nvironment_earth_universe/rock_cycle/acti vity/ Igneous Rocks • Igneous rocks are called fire rocks and are formed either underground (intrusive) or above ground (extrusive). Igneous Rocks • Igneous rocks are called fire rocks and are formed either underground (intrusive) or above ground (extrusive). • Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in pockets. As these pockets of magma cool slowly underground, the cooled magma becomes igneous rocks. Igneous Rocks • Also formed when volcanoes erupt, causing the magma to rise above the earth's surface (extrusive). When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground. Magma • Magma (molten rock) is mostly made up of eight common minerals of the earth's crust and form silicate minerals. – These silicate minerals include • • • • • • feldspars (plagioclase feldspar, potassium feldspar) quartz micas (muscovite, biotite) pyroxenes (augite) amphiboles (hornblende) olivine – These minerals make up over 95% of the volume of the common igneous rocks, making igneous rocks easy to identify. Extrusive Igneous Rock Extrusive igneous rocks form when magma reaches the Earth's surface a volcano and cools quickly. Most extrusive (volcanic) rocks have small crystals. Examples include basalt, rhyolite, and andesite. Intrusive Igneous Rock Intrusive, or plutonic, igneous rocks form when magma cools slowly below the Earth's surface. Most intrusive rocks have large, wellformed crystals. Examples include granite, gabbro, and diorite How to tell if you have an igneous rock… • Igneous rocks are recognized by: – – – – – the interlocking texture of the grains the presence of vesicles (holes) in extrusive igneous rocks may be dark-colored and heavy may display two grain sizes, one much larger than the other Glassy Bowen’s Reaction Series http://youtu.be/R4X8ukSpbQo Texture- size and arrangement of crystal grains in igneous rocks Determined by the rate at which magma cools For example magma that cools very quickly can take on a glass like appearance as in Obsidian Steps in Identification Use Bowen’s Scale to determine identity of igneous rocks. 1. Determine the color (indicates mineral composition) 2. Determine the texture (indicates cooling history) – Phaneritic=large grains – cooled slow – Aphanitic=small grains- cooled fast (too small to identify with the naked eye) – Porphyritic=fine grains mixed with larger grains – Glassy=glass-like – Vesicular=holes Ex. A light-colored, Coarse-grained rock=granite http://youtu.be/3Hv17gNvnrM 28 m video Igneous Rock Bowen’s Reaction Series – defines the order in which minerals crystallize from magma -different minerals melt and crystallize at different temperatures http://youtu.be/R4X8ukSpbQo Bowen realized crystallizing process, can follow 2 paths. Discontinuous series contains minerals high in iron and magnesium which causes the minerals to crystallize differently. Continuous reaction series has minerals high in plagioclase the slightly different concentrations of minerals is responsible for the 2 different pathways Textures INTRUSIVE Coarse grained (phaneritic): Slow cooling EXTRUSIVE Fine grained (aphanitic): Fast cooling Porphyritic: Two phases of cooling: one very slow, one slow Porphyritic: Two phases of cooling: one slow, one fast Pegmatitic: Slow cooling plus high water content Glassy: Fast cooling plus high silica content 3rd Type – Volcanic – vesicular (bubbles/holes) Igneous Composition • Ultramafic rocks dominated by mineral olivine less than 45% silica • Mafic rocks are dominated by plagioclase and pyroxene • Mafic = Magnesium + Ferric (Iron) • Intermediate rocks are roughly even mixtures of felsic minerals (mainly plagioclase) and mafic minerals (mainly hornblende, pyroxene, and/or biotite). There is little or no quartz. • Felsic rocks are mostly feldspar (especially K-feldspar), at least 10% quartz, greater than 63% SiO2 INTRUSIVE COMPOSITIONS Peridotite Ultramafic -Green T e m p e r a t u r e Gabbro Mafic- Dark Magnesium Ferric EXTRUSIVE COMPOSITIONS Rare occasions only. We will not learn these. Basalt Mafic Diorite Andesite Intermediate Intermediate Granite Rhyolite Felsic - Light Felsic Mineral Composition- mostly determined by % of Silicate SiO2 felsic igneous rocks containing a high silica content, greater than 63% SiO2 (examples granite and rhyolite) intermediate igneous rocks containing between 52 – 62% SiO2 (example andesite and diorite) mafic igneous rocks have low silica 45 – 51% and typically high iron – magnesium content (example gabbro and basalt) ultramafic rock igneous rocks with less than 45% silica. (examples peridotite) http://youtu.be/cjyF-te4lQI Identifying Igneous Rocks