Igneous rocks are further classified according to; Describes the appearance of an igneous rock, based on the size, shape and arrangement of interlocking crystals. 1. Texture 2. Mineral Composition Is the mineral makeup of an igneous rock based on the chemical composition of the magma. Reference: Pages Classification of Igneous Rocks:

Igneous rocks are classified from n texture n mineral composition depends on: chemical makeup of parent magma depends on: how fast/slow magma cools

Igneous compositions mainly silicate minerals determined by composition of magma from which it crystallized magma mainly 8 elements: Si, O, Al, Ca, Na, K, Mg, Fe Most abundant constituents

The minerals that are present in any igneous rock depends on the chemical composition and the environment (temperature of the magma) from which the molten rock crystallizes.  Bowen also noted that minerals will react with the magma to produce the next mineral in the reaction series, this is known as Bowen’s Reaction Series.  N. L. Bowen discovered that different minerals form at different temp.  Ca-Rich Plagioclase Na-Rich Plagioclase Mafic Intermediate Felsic Igneous compositions

Olivine and Ca-rich plagioclase feldspar are the first to crystallize at very high temperatures and these minerals are often found in mafic igneous rocks.  Therefore, igneous rocks are classified according to their mineral makeup as Mafic, Intermediate, or Felsic.  Orthoclase feldspar and quartz crystallize at lower temperatures and are found in felsic igneous rocks  Ca-Rich Plagioclase Na-Rich Plagioclase Mafic Intermediate Felsic Igneous compositions

Magma è cools è solidifies è forms silicate minerals Two major silicate mineral groups: DARK silicates LIGHT silicates Igneous compositions

DARK LIGHT Rich in Fe and/or Mg Si, K, Na, Ca Poor in Si Fe and/or Mg Silicate group olivine pyroxene amphibole biotite quartzmuscovitefeldspars F orthoclase F plagioclase Examples Igneous compositions

Igneous rocks types n mafic n felsic F High in Si. F Lighter and Less Dense F Found in Continental Crust F High in Mg and Fe. F Dark and Dense F Found in Ocean Crust ma gnesium + fe rrum fel dspar + si lica (quartz) Igneous compositions

Mafic Composition basalt gabbro m a f i c m a f i c zooming in volcanic plutonic

 contain magnesium and iron rich minerals  form at high temperatures 1200 E C  found mainly in oceanic crust  form most volcanic rocks (Basalt)  low percentage of silica, very fluid magmas  forms dark colored minerals, thus rocks are dark color  minerals include; olivine, pyroxene, plagioclase. feldspar Mafic Composition

andesite diorite i n t e r m e d i a t e i n t e r m e d i a t e zooming in volcanic plutonic Intermediate Composition

 contains 25% dark silicate minerals (Amphibole, Pyroxene,. and Biotite Mica)  forms at moderate temperatures, approximately 800 E C  found associated with volcanic activity confined to the ….margins of the continents  form mainly volcanic intermediate rocks (Andesite)  high percentage of silica, very viscous (thick) magmas  contains both light and dark colored minerals  minerals include; Amphibole, Pyroxene, Biotite Mica and. Plagioclase Feldspar Intermediate Composition

granite rhyolite zooming in f e l s i c f e l s i c plutonic volcanic Felsic Composition

obsidian pumice f e l s i c f e l s i c volcanic Felsic Composition

 contains orthoclase feldspar and quartz (silica)  forms at lower temperatures, approximately 600 E C  found mainly in continental crust  form mainly plutonic rocks (Granite)  high percentage of silica, very viscous (thick) magmas  forms light colored minerals, thus rocks are light colored  minerals include; orthoclase and plagioclase feldspars,. quartz, and muscovite mica Felsic Composition

3 main types è basaltic è andesitic è granitic “felsic” “mafic” magnesium + ferrum high in Mg, Fe. Dark, dense feldspar + silicate high in Si, lighter, less dense Igneous Magma Compositions

è basaltic è andesitic è granitic “felsic” “mafic” magnesium + ferrum high in Mg, Fe. Dark, dense feldspar + silicate high in Si, lighter, less dense “felsic” 3 main types Igneous Magma Compositions

Classification Chart Mineral Composition Plutonic Volcanic

Sample Problem Explain how mineral composition could be used to classify igneous rocks. Answer: Mineral Composition: If the igneous rock is light color and consist of the minerals quartz and orthoclase feldspar, it is classified as felsic. If the igneous rock is dark color and consist of the minerals pyroxene and plagioclase feldspar, it is classified as mafic.