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Igneous Rocks What’s behind Mt. Rushmore Igneous Rocks Magma vs. Lava Magma – Molten (melted) rock – Gases – Mineral crystals – Beneath the surface Lava – Magma on the surface Composition of Magma Elements O, Si, Al, Fe, Mg, Ca, K, Na Compounds SiO2 - Silica – Most abundant – Greatest effect on magma characteristics Composition of Magma Basaltic Magma 50% Silica Oceanic Lithosphere Andesitic Magma 60% Silica Granitic Magma 70% Silica Continental Lithosphere Mineral Composition Felsic Form from granitic magma – Continental Lithosphere Light-colored – Gray, white, pink High silica content Low iron and magnesium Mineral Composition (cont.) Intermediate Forms from andesitic magma Dark & Light-colored – 50/50 – Half black/half white Moderate levels of silica content and iron and magnesium DOES NOT HAVE K-SPAR – No pink Mineral Composition (cont.) Mafic Forms from basaltic magma – Oceanic Lithosphere Dark-colored – Black/dark green Low silica content High iron and magnesium Environment of Formation Intrusive Magma inside the earth Cools slowly Large crystals Extrusive Lava on surface Cools quickly Small crystals (if any) Texture Glassy Non-crystalline Fine Less than 1 mm Coarse 1mm to 10 mm Very Coarse 10 mm or larger } } Extrusive Intrusive Texture (cont.) Vesicular Has gas pockets Non-vesicular No gas pockets Some Igneous Rocks Are Named on Textural Criteria Pegmatite – Extremely large crystals Pumice - Porous Obsidian - Glass Tuff - Cemented Ash Porphyritic Texture Large well-formed crystals surrounded by small finer-grained crystals Complex cooling history Cools slowly – Creating large crystals Then cools very fast – Creating small crystals Granite: The Wisconsin State Rock Obsidian Vesicular Basalt Felsic Inter Scoria (red) Mafic Sedimentary Rocks Origin of Sedimentary Rocks Erosion Creating of sediments Physical and chemical weathering Transportation Sediments are brought together Origin of Sedimentary Rocks Deposition Water deposition commonly forms layers – Sorting Glaciers and landslides do not create layers Burial To create heat and pressure Lithification Cementing (gluing) together of sediments – Making sedimentary rocks Sedimentary Structures Bedding – Layers of Rock Graded Bedding – largest on the bottom and smallest particles on the top Sedimentary Structures Bedding – Layers of Rock Horizontal Bedding – Layers deposited horizontally Sedimentary Structures Bedding – Layers of Rock Cross Bedding – Layers at angles Sedimentary Structures Ripple Marks Symmetrical Beach Water movement in two directions Sedimentary Structures Ripple Marks Asymmetrical Stream Water movement in one direction Not this “One Direction” Types of Sedimentary Rocks Clastic Sediments glued together Clastic = “pieces” Greek Chemical Precipitation of dissolved minerals in water Organic Accumulation of remains of once living things Clastic Sedimentary Rocks Coarse-Grained Clastics Gravel sized particles Transported by high energy flows Conglomerates – Gravel-sized rounded particles – Transported great distances Breccias – Gravel-sized angular particles – Transported short distances Clastic Sedimentary Rocks Conglomerate Breccia Clastic Sedimentary Rocks Medium-Grained Clastics Sand sized particles High Porosity – % of open space – Can contain fluids Groundwater, air, natural gas, and oil Clastic Sedimentary Rocks Fine-Grained Clastics Siltstone Shale Low porosity – Particles are too small Chemical Sedimentary Rocks Minerals dissolve during chemical weathering Carried to lakes and oceans Water evaporates, minerals are supersaturated, and precipitate out – Called evaporites Calcite, halite, and gypsum Organic Sedimentary Rocks Limestone Calcite from sea organisms’ shells – Reacts with acid – Coal Lithification of plant remains Organic Sedimentary Rocks Limestone Coal Sedimentary Rock Identification Sedimentary Rock Identification Rounded Conglomerate Angular Breccia Grains larger than gravel Does NOT react with acid Grains Visible Grains smaller than gravel Grains Not Visible Layered Black, shiny, lightweight Pink, white, clear, softer than fingernail Abundant fossils present, whole or broken Does react with acid Feels Gritty, Can’t see particle Pink, white, Conchoidal fracture, s many colors Sandstone Siltstone Chert Shale Coal Salty taste, cubic shape Pink, white, Halite Gypsum Fine-grained matrix with many fossils Fossil Limestone Porous, lightweight shell fragments, white to tan Coquina Sand grains held together by CaCO3 Limestone White/powdery Feels gritty Chalk Limestone Fine Grained May or may not see grains Micrite Limestone Metamorphic Rocks Metamorphic Rocks Metamorphism The mineralogical, chemical, and structural adjustment of solid rocks to the physical and chemical conditions imposed at a depth below the surface zones of weathering and cementation, which differ from the conditions under which the rocks were originated. Sedimentary and igneous rocks are changed due to pressure and heat or chemical reactions while remaining solid. Causes of Metamorphism Temperature Earth’s internal heat Igneous Intrusion Pressure Increases with depth – Vertical pressure from weight of overlaying rocks Mountain Building – Horizontal pressure form colliding plates. Chemistry Fluids flowing through the rocks react, forming new minerals Causes of Metamorphism Rocks change form while remaining solid If rock melts, it becomes… Magma, which will then produce… Igneous Rocks. “Metamorphism ends when a rock melts” Metamorphic Rocks Metamorphic Textures Foliated Have a banded appearance because the minerals in the rock are in parallel alignment An animation of metamorphic rocks forming Grades of Metamorphism Metamorphic Textures Foliated Metamorphic Textures Nonfoliated No banding Interlocking mineral grains – “THE MARSHMALLOW EFFECT” Metamorphic Textures Nonfoliated Foliated Metamorphic Rocks Grades of Metamorphism Metamorphic Rocks Igneous Sedimentary Metamorphic Igneous Sedimentary Metamorphic Crystals Sediments Foliated Cooling rate Gravel, sand, silt/clay Bands Mineral Composition Fossils Felsic, Intermediate, Mafic Glassy Layers Nonfoliated Crystals smooshed Vesicular Some react with acid together “Marshmallow Effect” The Rock Cycle The circular process by which each of the three major rock types is formed from the others The Rock Cycle The Rock Cycle Granite Sandstone Quartzite What Rocks Tell Us Rock Type How Classified What They Tell Us Felsic Continental Lithosphere Light Composition Intermediate 50/50 Tectonic Setting Mafic Igneous Oceanic Lithosphere Dark Intrusive Texture Slowly Magma Extrusive Cooling History Lava Chemical (PPT) DEEP Quickly Surface – Volcanic Erosion Sedimentary Structures Clastic (Pieces) Composition Boundary Between Surface Environment Water Organic (Fossils) Life Forms Present Large High Sedimentary Small Grain Size/Shape Rounded Composition Energy of Environment Low High Angular Low Quartzite Sandstone Marble Original Rock Type Slate Limestone Shale Metamorphic Foliated Texture Nonfoliated Degree of Change Low to High Low
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