Chapter 3 Matter and Minerals

1. Chapter 3Matter and Minerals

2. Minerals: Building blocks of rocks • By definition a mineral is • Naturally occurring • Inorganic • solid • Ordered internal molecular structure • Definite chemical composition • Rock • A solid aggregate of minerals

3. Composition of minerals • Elements • Basic building blocks of minerals • Over 100 are known (92 naturally occurring) • Atoms • Smallest particles of matter • Retains all the characteristics of an element

4. What are the most common elelments on earth? • oxygen is the big dog in town - it accounts for 46.6% of the earth's crust by mass (and 94% of it by volume!). • silicon at 27.7% of the crust by mass, we come up with the astounding realization that nearly 75% of the earth's crust is composed of silicon and oxygen. Wow! • The other six (6) elements are: • Aluminum . . . . . 8.1% • Iron . . . . . . . 5.0% • Calcium. . . . . . 3.6% Sodium . . . . . . 2.8% • Potassiun. . . . . 2.6% Magnesium. . . . . 2.1%

5. Most common minerals on earth

6. Silicates • Silicates • Consists of a small silicon atom with a +4 charge surrounded in tetrahedral fashion by four larger oxygen atoms each having a -2 charge. • Net charge on the anion group is -4. To satisfy this charge deficiency the SiO4tetrahedra can either bond with cations (Fe, Mg, Ca, K, Na) or join with other SiO4 tetrahedra through oxygen sharing.

7. Tetrahedron

8. Top 10 most common minerals • The Common Rock Forming Minerals • Feldspar (silicate) • Quartz (silicate) • Muscovite (silicate) • Ferromagnesians • Olivine (silicate) • Pyroxene (silicate) • Amphibole (silicate) • Biotite (silicate) • Muscovite (silicate) • Calcite (not a silicate)

9. Composition of minerals • Atomic structure • Central region called the nucleus • Consists of protons (+ charges) and neutrons (- charges) • Electrons • Negatively charged particles that surround the nucleus • Located in discrete energy levels called shells or valences.

10. Structure of an atom Figure 3.4 A

11. The maximum number of electrons that an atom can have in it’s valence shell is 8 it is not balanced until it has eight in it’s outer shell. The number of electrons in its valence shell corresponds to its group on the periodic chart.

12. Things to remember from chemistry: The nucleus of an atom is composed of _________ and __________ The atomic number is the same as the number of __________ A chemical element is defined by its number of __________ Atomic Mass is the mass of the ______ and _____ of an atom.

14. Composition of minerals • Chemical or Covalent bonding • Formation of a compound by combining two or more elements in other words the electrons are_______. • Ionic bonding • Atoms gain or lose outermost or ________electrons to form ions • Ionic compounds consist of an orderly arrangement of oppositely charged ions called ________

15. Halite (NaCl) – An example of ionic bonding Figure 3.6

16. Another name for Halite is ________ • It has an ionic bond • As we know this bond is not strong since we can easily dissolve it in water.

17. Composition of minerals • Covalent bonding • Atoms share electrons to achieve electrical neutrality • Generally ________than ionic bonds • Both ionic and covalent bonds typically occur in the same compound

18. Covalent bonding Figure 3.7

19. Composition of minerals • Other types of bonding • Metallic bonding • Valence electrons are free to migrate among atoms • Weaker and less common than other bonds

20. Isotopes : Composition of minerals • Isotopes and radioactive decay • Mass number = sum of neutrons + protons in an atom • _________= atom that exhibits variation in its mass number • Unstable _________emit particles and energy in a process known as radioactive decay

21. Structure of minerals • Minerals consist of an orderly array of _________chemically bonded to form a particular crystalline structure (meaning orderly) • Internal atomic arrangement in ionic compounds is determined by ionic size

22. Geometric packing of various ions Figure 3.8

23. Structure of minerals • Polymorphs • Minerals with the same composition but different crystalline structures • Examples include diamond and graphite • Phase change = one polymorph changing into another

24. Diamond and graphite – polymorphs of carbon Figure 3.10

25. Part 2 Physical properties of minerals • Primary diagnostic properties • Determined by observation or performing a simple test • Several physical properties are used to identify hand samples of minerals

26. Physical properties of minerals • Crystal form • External expression of a mineral’s internal structure • Often interrupted due to competition for space and rapid loss of heat

27. A garnet crystal

28. Cubic crystals of pyrite Figure 3.11 A

29. Physical properties of minerals • __________ • Appearance of a mineral in reflected light • Two basic categories • __________ • __________ • Other descriptive terms include vitreous (glassy), silky, or earthy

30. Galena (PbS) displays metallic luster

31. Physical properties of minerals • Color • Generally unreliable for mineral identification • Often highly variable due to slight changes in mineral chemistry • Exotic colorations of certain minerals produce gemstones

32. Quartz (SiO2) exhibits a variety of colors Figure 3.26

33. Physical properties of minerals • _________ • Color of a mineral in its powdered form • _________ • Resistance of a mineral to abrasion or scratching • All minerals are compared to a standard scale called the Mohs scale of hardness

34. Streak is obtained on an unglazed porcelain plate Figure 3.12

35. Mohs scale of hardness Figure 3.13

36. Physical properties of minerals • 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

37. Physical Properties of Minerals continued • Cleavage is described in terms of how easy the cleavage is produced. From easiest to hardest to produce the terms are: • perfect, imperfect, good, distinct, indistinct, and poor

38. Common cleavage directions Figure 3.15

39. Fluorite, halite, and calcite all exhibit perfect cleavage

40. Physical properties of minerals • _________ • Absence of cleavage when a mineral is broken • _________ • Weight of a mineral / weight of an equal volume of water • Average value = 2.7

41. Conchoidal fracture Figure 3.16

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

43. Mineral groups • Nearly 4000 minerals have been named • 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 over 98% of the continental crust

44. Elemental abundances in continental crust Figure 3.18

45. Mineral groups • Silicates • Most important mineral group • Comprise most rock-forming minerals • Very abundant due to large % of silicon and oxygen in Earth’s crust • Silicon-oxygen tetrahedron • Fundamental building block • Four oxygen ions surrounding a much smaller silicon ion

46. Two illustrations of the Si–O tetrahedron Figure 3.19

47. Mineral groups • Joining silicate structures • Single tetrahedra are linked together to form various structures including • Isolated tetrahedra • Ring structures • Single and double chain structures • Sheet or layered structures • Complex 3-dimensional structures

48. Three types of silicate structures Figure 3.21

49. Mineral groups • Common silicate minerals • Light silicates: Feldspar group • Most common mineral group • Exhibit two directions of perfect cleavage at 90 degrees • Orthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar) are the two most common members

50. Potassium feldspar Figure 3.24