Ch02_outline (1)

Ch02_outline (1) - Minerals: Building Blocks of...

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Unformatted text preview: 9/29/10 Minerals: Building Blocks of Rocks Ch.2 2010 2 ??? “Mineral”  Middle English, from  Medieval La<n minera le,  from neuter of minera lis, pertaining to mines 3 4 Earth system cycles Minerals: the building blocks of rocks  Defini<on of a mineral (p.31)  Mineraloid  ­ lacks an orderly internal structure •  Natural •  Inorganic •  Solid •  Possess an orderly internal structure of atoms •  Have a definite chemical composi;on Figure 1.21 5 6 1 9/29/10 Figure 2.3 [email protected] and structure of minerals  Elements •  Basic building blocks of minerals •  Over 100 are known •  92 naturally occurred •  98 %: O2, Si, Al, Fe, Ca, Na, K, Mg  Atoms •  Smallest par<cles of maZer •  Have all the characteris<cs of an element 7 8 D. I. Mendeleev   Arranging the 63 known elements into a Periodic Table based on atomic mass;  Published in “Principles of Chemistry” in 1869. Periods (7) Periodic table of the Elements Groups (18) 9 Figure 2.4 10 How atoms are constructed  Nucleus – central part of an atom that contains •  Protons – posi<ve electrical charges •  Neutrons – neutral electrical charges How atoms are constructed  Energy levels, or shells •  Surround nucleus •  Contain electrons – nega<ve electrical charges Figure 2.5 11 12 2 9/29/10 How atoms are constructed  Atomic number is the number of protons in an atom's nucleus 13 14 Forms a compound with two or more atoms that gain or lose •  Ionic compounds consist of an orderly electrons (valence) to form ions (Ionic bonding) arrangement of Bonding of atoms Covalent bonding •  Atoms share electrons to achieve electrical neutrality –  The electrons are shared • The electrons are transferred •  An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net posi;ve or nega;ve electrical charge. oppositely charged ions 15 16 Covalent bonding How atoms are constructed •  Other types of bonding •  Metallic bonding (v. 5 ­7) –  Valence electrons are free to migrate among atoms –  Weaker and less common than other bonds •  Generally stronger than ionic bonds •  Both ionic and covalent bonds typically occur in the same compound 17 18 3 9/29/10 Isotopes and radioac;ve decay •  Mass number = sum of neutrons + protons in an atom •  Isotope = atom that exhibits varia<on in its mass number •  Unstable isotopes emit par<cles and energy in a process known as radioac<ve decay Isotopes •  Have different mass numbers – the sum of the neutrons plus protons •  Many isotopes are radioac<ve and emit energy and par<cles 19 20 Structure of minerals •  Minerals consist of an orderly array of atoms chemically bonded to form a par<cular crystalline structure •  Internal atomic arrangement in ionic compounds is determined by ionic size Geometric packing of various ions 21 22 Structure of minerals •  Polymorphs •  Minerals with the same composi<on but different crystalline structures •  Examples include diamond and graphite »  Phase change = one polymorph changing into another 23 Diamond and graphite – polymorphs of carbon Figure 3.10 24 4 9/29/10 Minerals  Physical proper<es of minerals •  Crystal form •  Luster •  Color •  Streak •  Hardness •  Cleavage GEOD •  P.61 25 26 The mineral quartz oMen exhibits good crystal form Pyrite (fool’s gold) displays metallic luster 27 28 Sheet ­type cleavage common to the micas Mohs scale of hardness Amer Friedrich Mohs (1773– 1839), German mineralogist. 29 30 5 9/29/10 Common cleavage direc<ons exhibited by minerals Three examples of perfect cleavage – fluorite, halite, and calcite Cube: 3 at 90 Octahendron: 4 Rhombohedron: 3 not at 90 31 32 Physical proper<es of minerals •  Fracture •  Specific gravity •  Other proper<es • Taste • Smell • Elas<city • Malleability 33 Conchoidal fracture 34 Physical proper<es of minerals  Other proper<es •  Feel •  Magne<sm •  Double Refrac<on •  Reac<on to hydrochloric acid Magne<te Minerals  A few dozen minerals are called the rock ­forming minerals •  The eight elements that compose most rock ­forming minerals are • calcium (Ca), • sodium (Na), • potassium (K), • magnesium (Mg) •  Most abundant atoms in Earth's crust are oxygen (46.6% by weight) and silicon (27.7% by weight) • oxygen (O), • silicon (Si), • aluminum (Al), • iron (Fe), Calcite 35 36 6 9/29/10 Checkpoint [email protected] of [email protected] crust 37 38 Mineral groups The silicate (SiO4) ­4 molecule • Rock ­forming silicates • Most common mineral group • Contain the silicon ­oxygen tetrahedron (molecule) 39 40 . Common silicate minerals Mineral groups •  Rock ­forming silicates •  Groups based upon tetrahedral arrangement •  Olivine – independent tetrahedra •  Pyroxene group – tetrahedra are arranged in chains •  Amphibole group – tetrahedra are arranged in double chains 41 42 7 9/29/10 Pyroxene vs Amphibole •  Pyroxene: French pyroxène, from Greek pyr ­ + xenos stranger •  Amphibole: from Greek amphibolos ambiguous •  Nephrite jade, consists of a microcrystaline interlocking fibrous matrix of the calcium, magnesium ­iron rich amphibole mineral series tremolite (calcium ­magnesium) ­ ferroac<nolite (calcium ­ magnesium ­iron). The higher the iron content the greener the colour. •  Jadei<te, a rock consis<ng almost en<rely of jadeite, a sodium ­ and aluminium ­rich pyroxene. The gem form of the mineral is a microcrystaline interlocking crystal matrix. Jade 43 44 Hornblende – a member of the amphibole group Mineral groups •  Rock ­forming silicates •  Groups based upon tetrahedral arrangement •  Micas – tetrahedra are arranged in sheets •  Two types of mica are bio<te (dark) and muscovite (light) •  Feldspars  ­ Three ­dimensional network of tetrahedra 45 46 Mineral groups •  Rock ­forming silicates •  Groups based upon tetrahedral arrangement •  Feldspars •  Two types of feldspar are Orthoclase and Plagioclase •  Quartz – three ­dimensional network of tetrahedra Plagioclase feldspar 47 48 8 9/29/10 Potassium feldspar Nonsilicate minerals Mineral groups • Major groups • Oxides: ~ 400, metalic+O2 or hydroxyl (OH) e.g. hema<te, magne<te • Sulfides : ~600 Sulfur S+ metals • Sulfates: ~ 300 metals+Sulfate (SO4) • “Na<ve” elements: ~ 20 Au, Ag, Cu, Fe, C, S 49 50 [email protected] Copper Nonsilicate minerals •  Carbonates: ~ 200 metal + carbonates (CO3) •  A major rock ­forming group •  Found in the rocks limestone and marble •  E.g. Calcite •  Halite and gypsum are found in sedimentary rocks •  Many have economic value 51 52 Carbonates Mineral resources •  Reserves are already iden<fied deposits •  Ores are useful metallic minerals that can be mined at a profit •  Economic factors may change and influence a resource An underground halite (salt) mine 53 54 9 9/29/10 End of Chapter 2 10 ...
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