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