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A toms and Minerals

Magnet and Iron and slide. A toms and Minerals. Quartz SiO 2 common mineral. Minerals: Building blocks of rocks. Definition of a mineral : Naturally occurring Inorganic solid Ordered internal molecular structure Definite chemical composition Definition of a rock :

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A toms and Minerals

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  1. Magnet and Iron and slide Atoms and Minerals Quartz SiO2 common mineral

  2. Minerals: Building blocks of rocks • Definition of a mineral: • Naturally occurring • Inorganic solid • Ordered internal molecular structure • Definite chemical composition • Definition of a rock: • A solid aggregate or mass of minerals

  3. Atomic structure • Central region called the nucleus • Consists of protons (positive charges) and neutrons (neutral charges) • Electrons • Negatively charged particles that orbit around the nucleus • Located in discrete energy levels called shells

  4. Flattened structure of an atom # protons (+) equals # electrons (-) Electrons in shells Number of outermost electrons determine types of bonding Argon Outermost (Valence) shell

  5. Some definitions: • Atomic number:number of protons in the nucleus • Atomic Mass: total mass of protons and neutrons within an atom’s nucleus • We can see these on a Periodic Table

  6. Periodic Table of the Elements # protons (+) equals # electrons (-) Electrons in shells Number of outermost electrons determine types of bonding Shows atomic number (# protons) and atomic mass (# protons + neutrons). Column shows # electrons in outermost shell

  7. Electrons are in shells. Octet Rule: Atoms larger than Hydrogen and Helium need 8 electrons in their outer shell for stability

  8. Neutral Atoms have #protons = # electrons Silicon has 4 electrons in Its outer shell Oxygen has 6 electrons in its valence shell

  9. To satisfy the octet rule atoms can gain or lose electronsIn that state they are called IONSThey can combine with oppositely charged ions to form neutral molecules Ions Oxygen, normally 6 valence electrons, wants 2 extra Silicon, normally 4 valence electrons, would like to be rid of, or share, 4

  10. Chemical Bonding 1: Ionic • Chemical bonding • Formation of a compound by combining two or more atoms • Ionic bonding • Atoms gain or lose outermost (valence) electrons to form ions • Ionic compounds consist of an orderly arrangement of oppositely charged ions • Usually Columns I (alkali metals e.g. Na) and VII (halogens e.g. Cl)

  11. Halite (NaCl)- An Example of Ionic Bonding Halite small Na+ large Cl- Table Salt Na+ Cl- Na+ Cl- Na+ Cl- Na+ Na+ Crystalline structure of Internal atomic arrangement is primarily determined by the size of ions involved NaCl Small Sodium ions between large Chlorine ions (a)

  12. Covalent bonding – sharing of valence electrons Cl2Chlorine gas Sharing Electrons in Outermost Shell

  13. Covalent Bonds in Water H2O Water is polar

  14. Other Bond Types • Metallic bonding • Valence electrons are free to migrate among atoms • Weaker and less common than ionic or covalent bonds • Intermolecular bonding • Hydrogen bonds- charged regions in water attract • Van der Waals bonds- electrons momentarily grouped on same side of nucleus

  15. Isotopes • Isotopes and radioactive decay • Atomic mass is the total mass of neutrons plus protons in an atom • An isotope is an atom that exhibits variation in its atomic mass, i.e. different numbers of neutrons • Some isotopes have unstable nuclei that emit particles and energy in a process known as radioactive decay. • 12C 13C stable 14C radioactive

  16. Structure of minerals • Polymorphs • Two or more minerals with the same chemical composition but different crystalline structures • Diamond and graphite (both carbon) are good examples of polymorphs • The transformation of one polymorph to another is called a phase change • Example: Graphite in a High Pressure Cell Makes Diamond • Some polymorphs make good PT indicators

  17. Diamond and graphite – polymorphs of carbon

  18. Physical properties of minerals • Crystal Form • External expression of the orderly internal arrangement of atoms The mineral garnet often exhibits good crystal form

  19. Physical properties of minerals • Luster • Appearance of a mineral in reflected light • Two basic categories • Metallic • Nonmetallic • Terms are used to further describe nonmetallic luster are vitreous (glassy), pearly, silky, earthy (like dirt), adamantine (greasy)

  20. Galena PbS displays metallic luster Valuable ore of Lead

  21. Physical properties of minerals • Color • Generally an unreliable diagnostic property to use for mineral identification • Often highly variable for a given mineral due to slight changes in mineral chemistry • Exotic colorations of some minerals produce gemstones • But we use it anyway Quartz (SiO2) exhibits a variety of colors

  22. Physical properties of minerals • Streak • Color of a mineral in its powdered form • Helpful in distinguishing different minerals with similar composition • Hardness • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs scale of hardness Streak

  23. Cleavage • Tendency to break along planes of weak bonding • Produces flat, shiny surfaces • Described by resulting geometric shapes • Number of planes • Angles between adjacent planes Micas have perfect cleavage Biotite Mica

  24. Three directions of perfect cleavage – fluorite, halite, and calcite Each Cleavage Plane is paired

  25. Physical properties of minerals • Fracture • Absence of cleavage when a mineral is broken. Shown: conchoidal fracture in Quartz • Specific Gravity • Ratio of the weight of a mineral to the weight of an equal volume of water • Average value is approximately 2.7 • Simply hefting a mineral works too.

  26. Physical properties of minerals • Other properties • Magnetism • Reaction to hydrochloric acid • Malleability • Double refraction • Taste • Smell • Elasticity

  27. Is it calcite or dolomite?

  28. Classification of Minerals • Nearly 4000 minerals have been identified on Earth (We discuss a few) • Rock-forming minerals • Common minerals that make up most of the rocks of Earth’s crust • Only a few dozen members • Composed mainly of the 8 elements that make up 98% of the continental crust

  29. Commonly formed Ion chargesoften called “oxidation state” Metals can form more than one Ion. Fe+2 is name Ferrous, Fe+3 is named Ferric

  30. Classification of Minerals • Silicates • Most important mineral group • Comprise most of the rock-forming minerals • Very abundant due to large amounts of silicon and oxygen in Earth’s crust • Basic building block is the silicon-oxygen tetrahedron molecule • Four oxygen ions surrounding a much smaller silicon ion

  31. The Component Atoms Silicon has 4 electrons in Its outer shell Oxygen has 6 electrons in its valence shell

  32. Remember: atoms can gain or lose electronsThey then combine with oppositely charged ions to form neutral molecules Ions Anion (negative) Cation (positive)

  33. Silicate Molecule 2_25 The Silicon-Oxygen Tetrahedron O2 - Si4+ O2 - O2 - The basis of most rock-forming minerals, charge - 4 O2 -

  34. Silicate Bonding I • Oxygen Oatoms may obtain electrons from Si atoms, producing the SiO4 -4 Ion. • The negative charge is balanced by positive metal ions. • This occurs in Olivine, (Fe,Mg)2SiO4, a high temperature Fe-Mg silicate. Forms of this mineral are stable 100’s of kilometers below Earth’s surface. • Sort of Ionic Bond

  35. Positive ion Tetrahedron facing down Tetrahedron facing up Fe and Mg Example OLIVINE SiO4-4 Ion Independent tetrahedra

  36. Silicate Bonding II • Alternately, the oxygen atoms may complete their outer electron shells by sharing electrons with two Silicon atoms in nearby silicon tetrahedra. • A sort of covalent bond

  37. A Pyroxene Single chains weakly paired

  38. 2_26c An Amphibole Positive ion Cleavages 56 and 124 deg Double chains (c)

  39. Example: Mica Sheet silicates (d)

  40. Clay Minerals(at high magnification) note sheet structure Very small crystals Kaolinite(hand specimen) Clays are also Sheet Silicates, just as Micas are Vietnam Anecdote

  41. Example: Quartz SiO2 2_26e Framework silicates (e) (3-D, also the Feldspars)

  42. Classification of Minerals • Common Silicate minerals • Feldspar Group • Most common mineral group • two directions of perfect cleavage at 90 degrees • In Feldspars, some of the Silicon atoms (oxidation state +4) are replaced by Aluminum (oxidation state +3) • Ion is not symmetrical • Pearly Luster A Potassium Feldspar

  43. Feldspars that use Calcium (Ca) or Sodium (Na) metals to balance the SiO4- 4 and AlO4-5 charges are called: Plagioclase feldspar Note the Twinning, seems to have ‘stripes’

  44. Summary

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