CHAPTER 3 SECTION 2 IGNEOUS ROCKS From the core of the continents to nearly all of the oceanic crust—igneous is everywhere!

 Formed from cooled/hardened _________ or ______  Are called _______________ [ignis  Latin fire]  The rate of __________ determines the size of the mineral’s crystals. “fire” rocks magma lava cooling andesite basalt pumice

INtrusive : below ground  cools slower  many many & large crystals Ex: granite, gabbro

 Visible due to erosion & weathering  Magma= mainly silicon & oxygen Gases: water vapor (gases trapped)  Magma less dense than surrounding rock  moves towards surface & cools Elements combine  minerals form & ‘grow’  crystals!  Example:  Granite  Cumberlandite

 Only found in Cumberland, RI (official state rock) 4-acre lot in Blackstone Valley (Iron Mine Hill) & trace amts. Narr. Bay  Dense & prone to rust (iron  magnetic); titanium, transitions to peridotite (intr. coarse ign.)  Formed 1.5 bya  volcanic activity  Valuable  cannon and farm tools 18 th /19 th cent.

Obsidian Air bubbles are sometimes trapped (pumice, scoria) Basalt EXtrusive : above ground  cools quicker  f e w & small crystals

 Magma = below ground// Lava= above ground Lava  most gases escaped  Lava hardens  extrusive igneous rock Extruded onto surface Example: Rhyolite, Basalt Basalt

 Classification based on two major characteristics: 1. Texture: appearance based on size, shape & arrangement of crystals 2. Composition: proportions of light and dark minerals

 Coarse-grained: slow cooling  large crystals  Allows charged atoms (ions) to move large distances within magma & link together (crystallize)  Fine-grained: rapid cooling  small crystals  Ions lose motion and quickly combine; all compete for available ions  Glassy: lava on surface  little time for ions to crystallize  randomly distributed  glassy appearance (tiny crystals)  Porphyritic: different-sized minerals experience different rates of cooling Large crystals (phenocrysts) may be surrounded by fine grained minerals Minerals don’t same rate (location and melting point.)

 Granitic : light-colored silicates (quartz & feldspar) 70 % silica 10 % dark silicate minerals (i.e. biotite mica, amphibole) Major component of continental crust Ex: rhyolite = extrusive granitic rock  Basaltic : contain many dark silicate materials (plagioclase feldspar) Rich in magnesium and iron  Iron  darker and denser than granitic rocks Ex: gabbro = intrusive basaltic rock  Andesitic : composition between granitic and basaltic Volcanic rock = andesite:  At least 25 % dark silicates (amphibole, pyroxene, biotite mica)  Dominant mineral plagioclase feldspar :type of feldspar dark w/ridges (striations)  Ultramafic : composed almost entirely of dark silicate minerals Earth’s surface  Ex: peridotite—upper mantle composition