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Minerals

Minerals. Building Blocks of Rocks and Economic Resources GLY 2010 - Summer 2012 Lecture 4. Minerals. Minerals are a major building block of most rocks Their properties determine a good part of the physical behavior of the earth. Mineral Definition. Naturally occurring Inorganic

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Minerals

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  1. Minerals Building Blocks of Rocks and Economic Resources GLY 2010 - Summer 2012 Lecture 4

  2. Minerals • Minerals are a major building block of most rocks • Their properties determine a good part of the physical behavior of the earth

  3. Mineral Definition • Naturally occurring • Inorganic • Crystalline

  4. Crystal Structure Examples Halite Fluorite

  5. Formation of Halite

  6. Atoms

  7. Atomic Terminology • The atomic number equals the number of protons. • Thus Hydrogen, with one proton, has atomic number 1, and iron, with twenty-six protons, has atomic number 26. • The atomic weight equals the number of protons plus the number of neutrons. • If an iron atom has 26 protons, and 30 neutrons, it has an atomic weight of 56.

  8. Chemical Elements • An element is composed of atoms with the same atomic number • Each element has a unique chemical symbol

  9. Isotopes • An isotope of an element is an atom with the correct number of protons for that element, plus a fixed number of neutrons • Example: Carbon has three isotopes, each with six protons, and with 6, 7, or 8 neutrons

  10. Stable or Radioactive • An isotope may be stable or radioactive • Carbon isotopes with 6 or 7 neutrons are stable, while the isotope with 8 neutrons is radioactive

  11. Chemical Symbols • Atomic number is shown as a subscript before the element symbol - 1H • The atomic weight is shown as a superscript before the symbol - 56Fe

  12. Examples of Chemical Symbols • Particular isotopes are shown using a superscript in front of the symbol • 1H is normal hydrogen, with one proton and no neutrons • 2H is deuterium, with one proton and one neutron • 3H is tritium, with one proton and two neutrons - it is radioactive

  13. Ions • Ions are charged particles • Cations: Atoms that lose one or more electrons become positively charged • Anions: Atoms that gain one or more electrons are negatively charges • Ionic charge: Shown by a superscript after the chemical symbol, O2-

  14. Use of Isotopes • Chemical tracers • Study topics such as: • Pollution • Formation temperature • The path of volcanic emissions, etc • Radioactive isotopes are used in estimating the age of materials

  15. Compounds • Combination of two or more atoms • Combination is called a molecule • Water H2O • Carbon dioxide CO2

  16. Molecules • Molecules may consist of just one element • Oxygen in the atmosphere is O2 • Molecules may consist of several elements, in various amounts • Example: Plagioclase feldspar, the most common mineral on earth NaAlSi3O8 - one sodium (Na), one aluminum (Al), three silicons (Si), and eight oxygens (O)

  17. Chemical Bonds • The “glue” that holds materials together • Responsible for the properties of matter • On an atomic scale • At the scale of the earth • When two atoms combine to form a chemical bond, energy is released

  18. Types of Bonds • Ionic • Covalent • Metallic • Hydrogen • Van der Waals

  19. Ionic Bonds • Bonds between a cation and an anion • They occur when a cation donates one or more electrons to an anion • They are strong • Dissolve in water • Halite, or table salt, for example

  20. Covalent Bonds • Equal sharing of electrons by two atoms • Very strong bonds • Compounds usually not soluble • May create molecules that do not readily combine to form larger particles • Ex. Carbon dioxide is strongly bonded within the molecule, but weakly bonded between molecules, so it is a gas

  21. Metallic Bonds • Outer electrons are loosely held • Properties: Opaque, may have a metallic luster • Bond strength is moderate

  22. Hydrogen Bonds • Secondary bond between oxygen on one water molecule and hydrogen on another Hydrogen bonding in water

  23. Van der Waals Bonds • Residual, extremely weak bonds form by distortion of electron clouds by the presence of a nearby atom Diamond Graphite

  24. Molecular Properties • Molecules - as strong as the weakest bonds within themselves

  25. Mineral Properties • Depend on the type and strength of bonds and number of bonds (bond density) within themselves • Minerals will be examined in the laboratory, and most properties will be taught there • Examples of mineral properties: hardness, cleavage

  26. Hardness • A mineral’s hardness is measured by the ability of a surface to resist abrasion

  27. Moh’s Scale of Hardness • Any higher number mineral will scratch any lower number. • Moh’s scale is not linear – the difference in hardness between low numbers is much less than between high numbers

  28. Cleavage • When a mineral always or usually breaks along a particular plane, it is said to have a cleavage plane

  29. Two-directional Cleavage • Selenite, a variety of the mineral gypsum, shows cleavage in two directions

  30. Angle Between Cleavage Planes

  31. Three-directional Cleavage • Halite, common table salt, shows three directions of cleavage at right angles

  32. Three-directional Cleavage • Calcite shows three directions of cleavage, not at right angles

  33. Four Directional Cleavage

  34. Crystal and Crystal Faces Apatite, showing a hexagonal prism - these are crystal faces, not cleavage planes

  35. Identification of Minerals • Minerals are identified based on their physical and chemical properties • A combination of properties are needed, just as no single line from a fingerprint can identify a person

  36. Mineral Classification • Classification is based on anion type • Minerals with the same anions have similar properties, while those with the same cations often do not

  37. Anions • Anions may be a single ion • Ex. Oxygen O2- • Anions are often groups of atoms, with the entire group having a negative charge • Ex. Carbonates are CO32- , one carbon with three oxygens, and the whole group with a minus 2 charge

  38. Common Anion Groups • Silicates, SiO44- • Oxides, O2- • Sulfides, S2- • Carbonates, CO32- • Phosphates, PO43-

  39. Occurrence of Minerals • Over half of all known minerals are silicates, because oxygen is the most common element on earth, and silicon is the second most common. • Silicates are the most important type of rock-forming minerals, those minerals that make up most of the earth’s rocks • Most silicate minerals contain other elements in addition to silicon and oxygen

  40. Silicon Tetrahedron • The SiO44- tetrahedron is the basic building block of silicate minerals

  41. Silicate Structures

  42. Chemistry of the Continental Crust • Eight elements account for almost all of the earth’s crust • Chart is based on weight percent • Oxygen is the most abundant, and silicon the second, which is why most minerals are silicates

  43. Felsic Minerals • Minerals with a lot of aluminum and silicon are light in color, and are called Felsic • Plagioclase feldspar, the most common mineral in the earth’s crust

  44. Mafic Minerals • Minerals with more iron and magnesium, and less silicon, are dark in color and are called Mafic (from the first two letters of magnesium and the first letter of ferium) • Augite, a type of pyroxene

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