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1 M a t t e r & M i n e r a l s Chapter 3. 2 Minerals Study of minerals = mineralogy.

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Presentation on theme: "1 M a t t e r & M i n e r a l s Chapter 3. 2 Minerals Study of minerals = mineralogy."— Presentation transcript:

1 1 M a t t e r & M i n e r a l s Chapter 3

2 2 Minerals Study of minerals = mineralogy

3 3 Minerals Basic building blocks of the crust By definition, a mineral must - 1. Occur naturally 2. Be inorganic 3. Be a solid 4. Have an orderly internal (crystal) structure, & 5. Have a definite chemical composition

4 4 Examples of Minerals Quartz SiO 2 Gold Au Gypsum CaSO 4. 2H 2 O Diamond C Ice H 2 0 About 4,400 minerals have been named

5 5 Examples of Non- Minerals Coal Petroleum Synthetic Diamonds, Rubies, Sapphires, etc. Opal (a mineraloid)

6 6 Rocks A quick view A mass of mineral or mineral-like matter occurring naturally as part of a planet May consist of only one mineral; usually more than one More details in later chapters

7 7 Composition of Minerals Minerals are made of Elements –Elements are the basic building blocks of minerals –112 are known / 92 occur naturally Elements are made of Atoms Atoms consist of electrons, neutrons, protons

8 8 Atomic Structure (Fig. 3.4) Nucleus –Protons –Positive electrical charge (+) –Neutrons –Electrically neutral Shells –Electrons –Negative electrical charge (-)

9 9

10 10

11 11 Atomic Structure Atomic Number –Number of protons in the nucleus Defines a specific Element Atoms are electrically neutral –No. of Protons = No. of Electrons Electrons in the outermost shell are called “valence electrons”

12 12 Chemical Bonding 8 valence electrons (VE) bring stability –Noble gases (Neon, Argon, etc.) Octet Rule –Most atoms bond with others to have 8 VE Atoms bond chemically by either –Gaining electrons –Loosing electrons, or –Sharing electrons

13 13 Ions & Types of Bonds Ions (electrically charged atoms) –Anion Negatively charged by gaining electrons –Cation Positively charged by loosing electrons Ionic Bond (Fig. 3.5) –Ions held together by electrostatic forces –Ex: Sodium chloride

14 14

15 15 Covalent Bond –Atoms bond by sharing electrons –2 Chlorine atoms share two electrons –Silicon & Oxygen form covalent bond –Carbon atoms bond covalently to form diamond & graphite

16 16

17 17 Hybrid Bond –Combination of Ionic and Covalent bonds Metallic Bond –Free floating electrons are shared by all

18 18 Isotopes & Radioactive Decay Atomic number –No. of protons in the nucleus Mass number –No. of neutrons + no. of protons Isotope –Same atomic number but different mass number –For example, Carbon 12, 13 & 14

19 19 Radioactive Decay Some isotopes are unstable and disintegrate naturally (they decay) Decay gives off radiation (more on this later) Rate of decay is constant with time Radioactive decay can be used as a geological clock (again, more on this later)

20 20 Structures of Minerals Internal structure depends on –Size of the ions –Electrical charges on the ions –Shape of multi-atom ions

21 21

22 22 Polymorphs –Minerals of same chemical composition but with different physical properties –Diamond & Graphite

23 23

24 24 Physical Properties of Minerals Primary Properties Crystal Form Luster Color Streak Hardness Cleavage Specific Gravity Secondary Properties Magnetism Taste Feel Smell Elasticity Malleability Double refraction Reaction to HCl

25 25 Physical Properties of Minerals Crystal Form The external expression of the internal arrangement of atoms – we’re lucky to see this Luster Appearance in reflected light –Metallic –Nonmetallic: vitreous, pearly, silky, earthy, etc. Color Varies in most minerals, constant in some

26 26 Pyrite (fool’s gold) Metallic Brassy color Cubic crystals Quartz Nonmetallic Colorless (can be many other colors) Hexagonal crystals

27 27 Physical Properties of Minerals Streak Color of the powder on a streak plate (unglazed porcelain tile), or of the powdered mineral Hardness Resistance to abrasion Mohs scale of hardness (relative) Absolute hardness

28 28

29 29 Mohs Scale of Hardness 1. Talc 2. Gypsum 3. Calcite 4. Fluorite 5. Apatite 6. Orthoclase 7. Quartz 8. Topaz 9. Corundum 10. Diamond Made up of 10 relatively common minerals

30 30 penny – pre-1982 (why?)

31 31 Physical Properties Cleavage –A plane of weakness in the crystal structure along which it easily breaks. Ex: Mica Fracture –Minerals that do not exhibit cleavage when broken have fracture. Ex: Quartz

32 32 Perfect cleavage - mica

33 33 Specific gravity –Essentially, the mineral’s density –Ratio between the mass of a volume of mineral to the mass of an equal volume of water –Most common minerals have a specific gravity of 2.5 to 3

34 34 Some other properties, for fun Fluorescence –Discovered by accident by George Stokes –The reaction of certain minerals to ultraviolet radiation –High energy light (UV – the stuff that can cause sunburns) is converted to low energy light (the kind we can see) (we’ll leave the physics alone…) –This property has everyday applications (look above your head)

35 35 The minerals calcite, willemite, & franklinite. Under short-wave UV, the calcite appears red, the willemite green, and the franklinite black.

36 36 Pleochroism –Some minerals show a different color depending on which direction you look at it –Dichroism – you will see two colors –Trichroism – you will see three colors

37 37 A crystal of the gem Tanzanite (a variety of the mineral zoisite), viewed from three directions. “front” “side” “top”

38 38 Incandescent light Transmitted light sunlight The gem alexandrite (June birthstone) under different light sources

39 39

40 40 Mineral Groups About 4,000 minerals have been named 8 elements make up over 98% (by weight) of the continental crust Oxygen (46.6)Silicon (27.7) Aluminum (8.1)Iron (5) Calcium (3.6)Sodium (2.8) Potassium (2.6)Magnesium (2.1)

41 41 Mineral Groups Chemical groups based on the anions Silicates & Nonsilicates Si & O combine to form the building blocks of silicates Silicates account for >90% of the crust Igneous rocks are made mostly of silicates Many nonsilicates are economically important

42 42 Silicates All silicates contain Silicon (not silicone) & Oxygen The fundamental building-block of all silicates is the Si - O tetrahedron 4 O ions surround one Si ion (Fig. 3.19) SiO 4 -4 (electrical charge on SiO 4 tetrahedron is -4)

43 43 Silicon Oxygen

44 44 Silicate Structures SiO 4 tetrahedra can join together –Oxygen ions are shared between tetrahedra “polymers” Affects certain physical and internal properties of silicate minerals

45 45 Silicate Structures Single chains (Pyroxenes) Double chains (Amphiboles) Sheet structures (Mica) Framework structures (Quartz) Rings (Beryl [emerald]) Cations (Fe, Mg, K, Na, Al, Ca) neutralize charges on tetrahedra

46 46

47 47 Common Silicate Minerals Most silicates form as molten rock cools Minerals indicate formation history Common silicates in the earth’s crust –>50% feldspars –12% Quartz The “Light” & “Dark” Silicates (kinda like chicken…)

48 48

49 49 The “Light” Silicates Generally light in color Contain Al, K, Ca, Na (except quartz) No iron or magnesium minerals Specific gravity is about 2.7 Feldspars, Quartz, Muscovite (mica)

50 50 Feldspars (“aluminosilicates”) –Potassium feldspar group (K ion) Orthoclase & Microcline Light cream to salmon pink No striations –Plagioclase feldspar group (Na & Ca ions) White to medium gray Striations

51 51 Parallel to this line

52 52 Quartz –Hardness 7 –Resistant to weathering –No cleavage –Conchoidal fracture –Colorless when pure –Impurities make it white, gray, yellow, pink, purple, etc.

53 53 Muscovite mica –Clear with excellent cleavage –Insulator, capacitors, window/oven glass –Sparkles in nail polish Kaolinite (a clay; not a primary mineral) –Fine chinaware –Paper coating –Thicken milkshakes

54 54 The “Dark” Silicates Iron- and magnesium-bearing (ferromagnesian) minerals Dark color (green, black, brown, red) Specific gravity 3.2 - 3.6 –Olivine group –Pyroxene group (Augite) –Amphibole group (Hornblende) –Biotite mica –(Garnet group)

55 55 Nonsilicate Minerals Make up about 8% of the earth’s crust Divided into classes based on the anion –Carbonates (CO 3 2- ) –Halides (Cl -, F -, Br - ) –Oxides (O 2- ) –Sulfides (S 2- ) / Sulfates (SO 4 2- ) –Native elements –And others Economically important

56 56 Nonsilicate Minerals Calcite / Dolomite Halite (also a rock)/ Fluorite Hematite / Magnetite / Ice (also a rock) Galena / Pyrite / Chalcopyrite Gypsum / Barite Gold / Copper / Silver / Diamond / Sulfur / Platinum to cite but a few

57 57 Gemstones “Precious”: Diamond Emerald (Beryl) Opal Ruby (Corundum) Sapphire (Corundum) “Semi-precious”: Alexandrite (Chrysoberyl) Amethyst (Quartz) Garnet Jade (Jadeite or Nephrite) Topaz Turquoise

58 58 A gemstone/jewelry aside: four homophones (words that sound the same, but spelled differently, with different meanings) –Carrot –Caret –Carat –Karat

59 59 Carrot –A veggie –Bugs Bunny’s favorite food –They do come from the ground…..

60 60 Caret ^ (look at the “6” key on your computer keyboard)

61 61 Carat –A gemstone weight –Based on the carob seed (supposedly all have the same mass) –200 milligrams (0.2 grams) –Carat weight & size of a given gem will depend on the density of the mineral Rhodolite – 3.91 ct 10.9 x 8.7 mm

62 62 Karat –Measure of the purity of gold, scale of 0 to 24 –24 K = 100% –Why 24? I don’t know –Being replaced by millesimal fineness – parts per thousand of the metal in the alloy Natural gold crystals

63 63 A last bit of mineral fun …

64 64 Crystals of the mineral rutile – intergrown to form letters of the alphabet (use your imagination)

65 65 End of Chapter

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