Chapter 2 Minerals & Rocks

Transcription

1 Chapter 2 Minerals & Rocks 2.1 Mineral definition Ion substitution Crystal structure Mineral classification Mineral identification 2.2 Rocks Forming of 3-rock 3 types Rock cycle

2 What is a mineral???

3 2.1 Mineral definition แร ธาต หร อสารประกอบอน นทร ย ท เก ดข นตามธรรมชาต ม โครงสร าง ภายในท เป นระเบ ยบ ม ส ตรเคม และสมบ ต อ นๆ ท แน นอน หร อ เปล ยนแปลงได ในวงจ าก ด (พจนาน กรมศ พท ธรณ ว ทยา, 2530) Mineral: A naturally occurring homogeneous solid with a definite (generally not fixed) chemical composition and a highly ordered-atomic arrangement usually formed by inorganic processes To be a mineral >> naturally formed solid specific chemical composition characteristic crystal structure

4 Galena-calcite-fluorite

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7 Is snowflake a mineral?

8 Is sugar a mineral?

9 Mineraloid (Noncrystalline minerals): Natural occurring amorphous substance or minerallike material e.g. natural glass, resins, opal Amorphous: Substance that lack of internal atoms arrangement. Amorphous alloy Crystalline alloy

10 Fire opal vibrate.wordpress.com/2007/08/19/fire-opal/

11 snowflake obsidian freakingcat.com/.../moldavite-besednice-4.jpg moldavite

12 How can we study minerals???

13 Characteristics of minerals Composition: chemical elements present & their proportion Crystal structure: arrangement of atoms of chemical elements packed together in a mineral

14 Elements and Atoms Chemical elements: the most fundamental substances that matters can be separated by chemical means. 117 elements in total have been observed (2008) 94 elements occur naturally on Earth 80 elements have stable isotopes, namely all elements with atomic numbers 1 to 82, except elements 43 and 61 (technetium and promethium)

15 Elements with atomic numbers 83 or higher (Bismuth and above) are unstable and undergo radioactive decay The elements from atomic number 83 to 94 have no stable nuclei, but are nevertheless found in nature, either surviving as remnants of the primordial stellar nucleosynthesis which produced the elements in the solar system, or else produced as short-lived daughter-isotopes through the natural decay of uranium and thorium

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17 Atoms: the smallest subdivision of matter that retains characteristics of an element. It contains proton (positive electrical charge) and neutron (electrical neutral) in the massive nucleus and surrounded by electron (negative electrical charge) Electron mass is 1/1837 that of proton Rutherford's atomic model (1914)

18 Neil Bohr s atomic model (1920) js082.k12.sd.us/.../atoms/atoms_1.htm

19 Quantum model of an atom

20 Shape of s, p & d orbitals The orbitals are 3- dimensional and not precisely defined The charge density falls off sharply at a certain distance from the nucleus All s-orbitals are spherical 1s < 2s < 3s etc All p-orbitals are dumbell shaped in 3 directions in space 2p < 3p < 4p

21 Atomic number: number of proton, positive charge, that equal to number of electron in uncharged atom Mass number: summation of proton and neutron of an element. Elements that contain different numbers of neutrons called isotopes

22 Ion: atom that lost or gains electron(s) i.e. cation and anion. Metal elements tend to give electron and nonmetal elements tend to receive electron Energy require for removing first electron from neutral atom is first ionisation potential

23 What holds atom together???

24 Chemical bonds Ionic bond (electrostatic bond): the attraction between oppositely charged ions. Resulting in exchanging of metal atom (forming cation) to nonmetal atom (forming anion)

25 Covalent bond Covalent bond: or electron sharing bond is the strongest chemical bond. sharing of election when orbitals overlap Electrons in outer orbital are filled as in stable inert gas configuration. Hence ionic bonding also shares some electrons and covalent bond often contain electrostatic charge, therefore, the proportion of ionic to covalent character can be assessed by Electronegativity : a measure of ability of an atom to attract electron to itself. The greater different of electronegativity, the more ionic bonding

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27 Metallic bond atomic nuclei and nonvalence electron orbitals bound together by the aggregate electrical charge of a cloud of valence electron that surrounds the nuclei. Electron(s) ) belong to no particular nucleus and freely mobile through the structure or even out of it. Metallic luster, malleable, electron conductivity.

28 Van der Waals bond weak dipole attraction that forms by synchronizing of electrons motions in order to avoid each other as much as possible. This weak dipole, therefore, induce a similar effect on the adjacent atoms.

29 Polar bond Electrons distribution in some molecule causes charged or become polar e.g.water H 2 O. The side of the molecule with the hydrogens is slightly positive, the side with the O is slightly negative. The complete molecule is neutral. Water molecule is stable, yet it can appear to be charged, depending upons its orientation. This is why water can dissolve so many things, e.g. water dissolves NaCl

30 Hydrogen bond Hydrogen bonding is very important. It is a part of most biological substances. Covalent molecules are often terminated by H atoms. These molecules are held together by polar bonding of the H atoms. Example: wood, plastics, silk, candle wax, DNA. Egg white is clear because of hydrogen bonding. But heat it up and break the bonds, and you end up with a white gelatinous solid. Polar and hydrogen bonds are weak

31 2.1.1 Ionic substitution Substitution of an ion for another in a crystal structure Substitution factors are Ionic radius Ionic charge (Temperature)

32 Common ionic substitution in geologic materials S 2- Cl 1- Ionic charge O F 1- K 1+ Pb 2+ Ionic radius (nm) Na Ca Fe 2+ Li Mg 2+ Fe Al Si

33 Common ionic substitution in geology Mg 2+ Ca 2+ in calcite-dolomite Calcite [Ca(CO 3 ) 2 ] Dolomite [CaMg(CO 3 ) 2] Calcite, Dolomite on Sphalerite - Naica, Mexico

34 Mg 2+ Fe 2+ in olivine (Mg,Fe) 2 SiO 4 Forsterite (Mg 2 SiO 4 ) Fayalite (Fe 2 SiO 4 )

35 Na 1+ Ca 2+ in plagioclase (Na,Ca)AlSi 3 O 8

36 How do atoms live in a crystal?

37 ://darkwing.uoregon.edu/~cashman/geo311/311pages/l1-intro_pic_files/image014.gifgif

38 Crystal o Homogeneous solid possessing long-range three-dimensional internal order o Euhedral crystal o Subhedral crystal o Anhedral crystal wulfrenite

39 Subhedral crystal

40 anhedral crystal

41 2.1.2 Crystal structure geometric pattern that atoms arrange in a solid Diamond structure Quartz structure

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43 Motif

44 Lattice Motif

45 lattice Unit cell lattice lattice

46 Quartz structure

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48 Silicon tetrahedron/tetrahedra

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50 Crystal structure geometric pattern that atoms arrange in a solid

51 Graphite VS Diamond Structure

52 Crystal systems Isometric Hexagonal Tetragonal Orthorhombic Monoclinic Triclinic

53 Crystallographic axes and angles between axes Isometric system Hexagonal system

54 Orthorhombic system Tetragonal system

55 Monoclinic system Triclinic system

56 pyrite Isometric system a = b = c α=β=γ= 90 Hexagonal system beryl a 1 =a 2 =a 3 c a 1^a 2 ^ a 3 =120 β= 90

57 barite Orthorhombic system a b c α = γ = β =90 idocrase Tetragonal system a= b c α = γ = β =90

58 gypsum labradorite Monoclinic system a b c α = γ =90, β > 90 Triclinic system a b c α β γ 90