EES 1030 Lecture 3 Outline of Last Lecture I. Minerals: Building Blocks of Rocksa. Ordered internal structureb. Specific chemical compositionc. Naturally occurringd. Inorganic solide. Distinctive physical propertiesOutline of Current Lecture II. Igneous RocksIII. Crystallization of magma/lavaIV. The nature of magma/lavaV. Classifying Igneous rocksVI. Igneous TexturesVII. PumiceVIII. Minerals in Igneous RocksIX. Common MineralsX. Origin of MagmaXI. Decompression MeltingXII. Fluid-Induced MeltingXIII. Magmatic DifferentiationXIV.Magma Compositional VariationsCurrent LectureIgneous RocksIgneous rocks form by cooling and solidification of magma (molten rock).Magma is formed by melting of rocks in the hot deep curst and mantle.Magma at Earth’s surface is called lava.Crystallization of magma/lavaWater changes from liquid to solid at 0 degrees CelsiusMagma changes from liquid to solid over a temperature interval of 200-300 degrees CelsiusThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.As magma cools, different silicate minerals begin to crystallize and grow.Igneous RocksRocks formed from lava at Earth’s surface are called extrusive or volcanic rocks.Rocks formed from magma at depth are called intrusive or plutonic rocks.The Nature of Magma/LavaMagma consists of three components:Liquid portion is called melt.Solids, if any, are usually silicate minerals.Gases or volatiles include water vapor, carbon dioxide, and sulfur dioxide.At high pressures at depth in magma = dissolved in the melt.At low pressures near surface = form separate gas phase.Classifying Igneous RocksIgneous rocks classified/named based on: textureTypes of minerals chemical compositionTexture is used to describe the overall appearance of a rock based on the size, shape, and arrangement of interlocking minerals.Crystal size  cooling rate.Igneous Textures: AphaniticFine-grained rick. Crystals too small (<1 mm) to identify with naked eye.Rapid rate of cooling near surface: VolcanicMay contain vesicles (holes from gas bubbles)Igneous Textures: PheneriticCoarse-grained rock.Large visible crystals (c. 1 – 20 mm).Slow rate of cooling at depth: Plutonic.Igneous Textures: PorphyriticLarge crystals (phenocrysts) are embedded in a matrix of smaller crystals (groundmass)Minerals form at different temperatures.Igneous Textures: PegmatiticExtremely coarse-grained rock.Crystal sizes from several centimeters to several meters.Form in late stages of crystallization of magma when rick in fluids (H20)Igneous Textures: Pyroclastic or Fragmental texture:Produced by violent volcanic eruptions.Often appear more similar to sedimentary rocks.Tuff = ash-sized fragments (<2 mm)Volcanic breccia = particles larger than ashIgneous Textures: GlassyVery rapid cooling of lava, resulting rock is called obsidian.Used by many ancient cultures to make sharp blades and arrowheads.Pumice: frothy glassDepressurization forms bubbles in the magma as gases (water, CO2) exsolve, rapid cooling freezes the bubbles in glass.PumiceUses: 1. Abrasive: skin exfoliant, heavy-duty soap, stone washed jeans, etc.2. Cement additive  Pozzolan light weight sets underwater. Used by Romans.Density = Mass / VolumeWater = 1 g / cm3Most rocks = 2-3 g / cm3Pumice =?Minerals in Igneous RocksSilicon-Oxygen tetrahedron is the fundamental building block.Common MineralsComposition of magma: Si & O, plus Fe, Mg, Ca, Al, Na, K.Igneous rocks are composed primarily of silicate minerals.Dark, mafic, (ferromagnesian)Silicates: olivine, pyroxene, amphibole, and Biotite mica.Light, felsic (nonferromagnesian) Silicates: Quartz, muscovite, mica, and feldsparsIgneous rock compositions: broad division, proportion of light to dark silicate minerals.Granitic composition: Mainly light-colored silicates, Felsic (feldspar & silica) in composition, major constituent of continental crust.Basaltic composition: Dark silicates and calcium-rich feldspar, Mafic (magnesium & ferrum, for iron) in composition, major constituent of oceanic crust.Granite/(plutonic) Felsic Rhyolite/(volcanic)Diorite/(plutonic) Intermediate Andesite/(volcanic)Gabbro/(plutonic) Mafic Basalt/(volcanic)Chemical composition of magma: Example: SiO2 determines physical properties of magma.Controls on the style of a volcanic eruption:Effusive lava flow vs. explosive eruption.Magma viscosity & volatile gas content.Origin of MagmaBasaltic magma is the most common magma produced in the Earth.Basaltic magma forms by partial melting of the time Earth’sPartial melting means incomplete melting.How and Why the mantle melts is linked to Plate Tectonics.Origin of MagmaThe Earth’s Crust and Mantle are solid rocks.Earth’s Crust does NOT float on Mantle of molten rock.Magma ONLY forms in special places where conditions allow pre-existing solid rocks to melt.How do we generate molten rock (magma)?Three ways:1. Increase temperature (thermal)2. Decrease pressure (decompression)3. Add water (fluid-induced)Most magma formed from melting of mantle but some felsic rocks from melting of crust.Decompression MeltingA decrease in confining pressure causes a decrease in a rock’s melting temperature.Divergent plate margins alone mid-ocean ridgesFluid-Induced MeltingAdding volatiles (primarily water) causes rocks to melt at lower temperatures.Convergent plate margins along subduction zones.Minerals crystallize in a systematic fashion based on their melting points.Magmatic DifferentiationComposition of magma in chamber changes as crystals grow and are then removed by