Igneous_Rocks

Igneous Rocks Igneous Rocks  “Ignis” means fire  Rocks that are formed from cystallization of magma  Magma is molten rock  Lava is magma that is on the Earth’s Surface Igneous Rocks  Two Types of Igneous Rocks Extrusive (Exterior)  Intrusive (Interior)   Igneous rocks that solidify into rock beneath Earth’s surface  Coarse Grained  Cool Slowly  Granite Extrusive Igneous Rocks Extrusive (Exterior)  Igneous rocks that solidify into rock on Earth’s surface  Fine Grained  Cool Quickly Intrusive Igneous Rocks Intrusive (Interior)  Igneous rocks that solidify into rock beneath Earth’s surface  Coarse Grained  Cool Slowly  Granite Igneous Rock Formation Origin of Magma  Where does the heat come from that melts rocks?   Formation of Earth Heat from the decay of radioactive elements Factors that Affect Magma Formation    Temperature  Increases with depth Increases with depth Decreases melting point Pressure  Water Content   Mineral Composition  Different minerals, Characteristics of Magma   Slushy Mix of molten  Compounds in Magma rock, gases, and  Silica ( Si02) mineral crystals  Most abundant Common Elements  Greatest effect on         Oxygen (O) Silicon (Si) Aluminum (Al) Iron (Fe) Magnesium (Mg) Calcium (Ca) Potassium (K) Sodium (Na)   Magma Characteristics Effects melting temp Viscosity of Magma  Types of Magma  Based on amount of Silica    Basaltic Andesitic Rhyolitic Type of Magma Rhyolitic Andesitic Basaltic SiO2 Content 70% 60% 50% Melting Rocks  Question  Does a rocks melt like an ice cube, all at the same time? Melting Rocks  Rocks melt according to their melting points.  Example: Ice cube with wax  Which would melt first ice or wax?  This example is known as partial melting.   Partial Melting: some minerals melt at lower temperatures and other minerals remain solid Think of “stew” Fractional Crystallization Opposite of Partial Melting  Last to melt are first to solidify (crystallize)  Bowen’s Reaction Series  N.L. Bowen Canadian  1900’s  Stated that “as magma cools, minerals form in predictable patterns”  Known as Bowen’s Reaction Series  Bowen’s Reaction Series  Two Branches  Feldspars  Continuous, gradual change of mineral compositions abrupt change of mineral type  Iron-Rich Minerals  An Bowen’s Reaction Series Feldspars     Continuous Change First Feldspars are rich in Calcium (Ca) Sodium (Na) increases as cooling continues Last Feldspars to form are Sodium rich (Na) Iron Rich Minerals  Discontinuous Change    Magnesium (Mg) cools around 18000C, when olivine crystallizes, this continous up to 15570C. Now Pyroxene begins to form. All olivine that was formed is now turned to pyroxene Quartz is the last to form, because silica Why do we find Olivine? Four main groups of igneous rocks based on magma type/mineral composition  Felsic: high silica content, light colored, from thick & slow moving magma, contains low amounts of Ca, Fe, and Mg dominant minerals quartz, potassium rich feldspar   Ex: granite, pumice, rhyolite Magma Type:  Intermediate: moderate amount of silica, mixture of colors dominant minerals: sodium and calcium rich feldspar   Ex: andesite, diorite Magma Type:  Mafic: low silica content, dark colored, high levels of Fe & Mg formed from thinner, more fluid, & hotter magma than Felsic rocks dominant minerals hornblende, calcium rich feldspar   Ex: basalt, gabbro Magma Type:  Ultramafic: very low silica content, dark colors, high levels of Fe & Mg dominant minerals: olivine, pyroxene   Ex: peridotite, dunite Magma Type: Classifying Igneous Rocks  Igneous rock textures:   Crystal size is dictated by the rate of cooling of the magma body. A slower cooling rate results in larger mineral crystals being formed in the rocks as they cool. Porphyritic texture - Large crystals surrounded by fine grained rock. The rock initially cools slowly to form some large crystals and then cools quickly to form the fine grained rock surrounding them. The Scheme for Igneous Rock Identification A Brief Tour Crystal size Grain Size Description Igneous rocks have “Intergrown Crystals” Intergrown Intergrown Intergrown Not Intergrown Where it was formed Outside the volcano: Extrusive Inside the Earth: Intrusive Bubbles ? Yes= Vesicular Bubbles ? No=Non-vesicular Very Light Color NotVery Light Light Neither Light nor Dark Not Very Dark Very Dark Dark Darkest Lightest Density Very Light Medium Density Dense Very Dense Light Finding The Minerals Identify the rock. Unless you have other information, work in the middle of the rock’s box. This is the amount of Potassium Feldspar in the rock. This is the amount of Quartz in the rock. This is the amount of Plagioclase Feldspar in the rock. Use tick marks on a scrap paper to measure the percentage. Potassium Feldspar 25% Quartz 40% Practice Name a light-colored, fine-grained rock with no bubbles. Name a coarse-grained, dense rock. Igneous Rock Resources Ore Deposits  Building Materials  Other Uses  Ore Deposits    Veins: streaks of valuable metal within a mineral. Created when a metal-rich fluid, such as goldquartz, goes through fractional crystallization, the mineral (quartz) has a lower crystallization temp and thus solidifies before the gold. The gold remains liquid and settles between the quartz crystals forming “gold veins.” Pegmatites: veins with extremely large grain crystals. Creates some of the world’s most precious gems. Kimberlites: intrusions of magma cooled deep within earth’s crust. Usually find diamonds with kimberlites. Named after location of first discovery, Kimberly, South Africa. Building Materials  Many IR’s are used in building materials because of their interlocking crystals strength IR’s are fairly weather resistant  Ex: Granite – building  Ex: Basalt – crushed up to make gravel  Other Uses Pumice – cleaning and polishes  Obsidian  heated to make perlite, a soil additive that keeps soil loose.  scalpels – more precise and smoother than steel, but 10x the cost 