NAT. SCI. 3 – Earth Science and AstronomyCHAPTER II:Earth Materials and Time RONALDO T. BIGSANG, M.Sc.
OBJECTIVES • Give the different classes of minerals; • Distinguish one class of mineral from another; • Name some commercially important minerals; and • Identify some harmful and dangerous minerals.
MINERAL CLASSES • 3,500 known minerals in the Earth’s crust • minerals are classified according to their chemical elements • silicates -- silicon + oxygen (combination of Si + O) • i.e. quartz – SiO2 • carbonates -- carbon + oxygen (combination of C + O) • i.e. calcite -- CaCO3 • sulfates -- sulfur + oxygen (combination of S + O) • i.e. anhydrite -- CaSO4 • phosphates -- phosphorus + oxygen (combination of P + O) • i.e. apatite --- Ca5(F,Cl,OH)(PO4)3
MINERAL CLASSES • oxides --- contain oxygen (O) • i.e. --- corundum --- Al2O3 • sulfides --- contain sulfur (S) • i.e. galena --- PbS • halides --- contain halogens (F, Cl, Br, I) • i.e. halite --- NaCl • hydroxides --- contain hydroxyl ion (OH) • i.e. bauxite --- Al(OH)3▪nH2O • native elements --- contain one element only • i.e. gold --- Au
SILICATES • 92% of Earth’s crust • silicon and oxygen are the 2 most common elements in the crust; readily combine • NOTE: • 1 silicon + 4 oxygen atoms = strong bonds • all silicates has a silicate tetrahedron structure • most silicates combine with other elements in the crust (EXCEPT quartz)
ROCK-FORMING SILICATES • feldspar • plagioclase --- with Ca (i.e. basaltic ocean rocks) • alkali feldspar --- with K or Na (i.e. orthoclase; granitic continental rocks) • quartz • common in continental rocks • purely SiO2 (no other elements) Photo by (top) http://upload.wikimedia.org/; (middle) http://www.rocksforkids.com/; (bottom) http://www.statesymbolsusa.org/
ROCK-FORMING SILICATES • pyroxenes • basaltic ocean rocks • amphiboles and mica • common in granitic continental rocks • clay • make up shale (most abundant sedimentary rock) Photo by (top) http://depthome.brooklyn.cuny.edu/; (middle) http://koofers-static.s3.amazonaws.com/; (bottom) http://www.geol.umd.edu/
ROCK-FORMING CARBONATES • less common in the crust than silicates • form sedimentary rocks • part of the shells and exoskeletons of some organisms • calcite --- limestone • dolomite --- dolostone or dolomite rock
ROCK-FORMING CARBONATES calcite dolomite Photo by (left) http://www.pitt.edu/; (right) http://geology.com/
COMMERCIALLY VALUED MINERALS • ore minerals • sources of metals and other elements • gold and silver ores occur as one element • other metals are commonly bonded to other elements (i.e. Fe2O3, Al2O3, PbS, ZnS, HgS, etc) • industrial minerals • mined for purposes other than extraction of metals • examples • halite (table salt) • gypsum (plaster) • apatite (phosphate fertilizer) • limestone (cement) • native sulfur (sulfuric acid, insecticide)
Photos by http://www.google.com.ph/; apatite (top), gypsum (middle), limestone (bottom)
COMMERCIALLY VALUED MINERALS • gems • prized for its rarity and beauty rather than for industrial use • precious • diamond, emerald, ruby, sapphire • semi-precious • amethyst, agate, jasper, tiger’s eye, garnet, olivine, topaz, turquoise
COMMERCIALLY VALUED MINERALS Photo by http://cdn.teachersource.com/
HARMFUL & DANGEROUS MINERALS • asbestosis and lung cancer • asbestos is a group of minerals that crystallize as long, thin fibers • cancer-causing substance (carcinogen) • example: chrysotile • radon and cancer • radon is formed by the radioactive decay of uranium • uranium most common in granite and shale • acid mine drainage and heavy metal contamination • sulfide ore minerals (contain lead, zinc, copper, cadmium, mercury) • mining and refining without proper and adequate pollution control
HARMFUL & DANGEROUS MINERALS • silicosis • fatal inflammation and scarring of the lungs • ground feldspar and quartz (silica dust) • people in the mining, stonecutting, quarrying, building and road construction industry • black lung • similar to silicosis but caused by coal dusts • people in the coal mining industry