NAT. SCI. 3 – Earth Science and Astronomy
CHAPTER II:Earth Materials and Time
RONALDO T. BIGSANG, M.Sc.
MINERALS II:Classes and Importance
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)
Photo by http://bc.outcrop.org/
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
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