CEE 1030 1st Edition Lecture 2 Igneous Rocks form by cooling and solidification of magma molten rock Magma formed by rocks melting at the earth s surface Extrusive or volcanic rocks rocks formed from lava at the Earth s surface Intrusive or plutonic rocks formed from magma at depth Magma will contain some solids and some crystals Magma consists of three components liquid portion is called melt solids if any are usually silicate minerals gases or volatiles including water vapor carbon dioxide and sulfur dioxide at high pressures at depth in magma dissolved in the melt Classifying igneous rocks Igneous rocks classified named based on texture types of minerals chemical composition texture used to describe the overall appearance of a rock based on the size shape and arrangement of interlocking minerals size of crystals tells us quickly how it went from molten rock to lava Igneous textures Aphanitic fine grained rock Crystals too small to identify with naked eye Phaneritic coarse grained rock Large visible crystals Slow rate of cooling at depth Plutonic Porphyritic large crystals phenocrysts are embedded in a matrix of smaller crystals groundmass Minerals form at different temperatures These 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 Pegmatitic extremely coarse grained rock Crystal sizes from several cm to several m Form in late stages of crystallization of magma when rich in fluids Pyroclastic pyroclastic or fragmental texture Produced by violent volcanic eruptions Glassy very rapid cooling of lava Resulting rock is called obsidian used by many ancient cultures to make sharp blades and arrowheads another type of glassy rock pumice pumice really heavy but full of air bubbles Pumice uses 1 abrasive skin exfoliant heavy duty soap stone washed jeans etc 2 check power point silicon oxygen tetrahedron is the fundamental building block silicate minerals most important constituents of igneous rocks ones with iron and magnesium dark colored without lighter granitic mainly light colored silicates basaltic dark silicates and calcium rich feldspar Rhyolite volcanic Granite plutonic Diorite plutonic Andesite volcanic Magma viscosity and volatile gas content effects the outcome of volcanic eruptions Which of the following shows the correct order left to right of increasing magma viscosity power point basaltic magma is the most common magma produced in the Earth basaltic magma forms by partial melting of the Earth s mantle Earth s crust and Mantle are solid rocks Earth s crust does NOT float on mantle of molten rock Three ways that melt is generated in different places 1 increase temperature thermal 2 decrease pressure decompression 3 add water fluid induced decompression melting a decrease in confining pressure pp other main type of decompression when plates are moving together adding volatiles primarily water causes rocks to melt at lower temperatures convergent plate margins along subduction zones magmatic differentiation during crystallization the composition of the liquid portion of the magma continually changes composition of magma in chamber changes as crystals grow if you have a big enough eruption you can have a magma chamber single eruption changing composition Economically viable sources for many metals Ex chromium platinum gold copper nickel also diamonds