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 mForm 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 rockThree 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