1. Chapter 2: Minerals: the Building Blocks of Rocks
Tarbuck, Lutgens, Tsujita, Hicock, Earth: An Introduction to Physical Geology 3Ce
Chapter 2: Minerals: the Building Blocks of Rocks
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2. Minerals: The 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 mass of minerals
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3. The Composition of Minerals
Elements
Basic building blocks of minerals
113 are known now (90 naturally occurring)
Atoms
Smallest particles of matter
Retains all the characteristics of an element
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4. The Composition of Minerals
Atomic structure
Central region called the nucleus
Consists of protons (positive charges) and neutrons (no electrical charges)
Electrons
Negatively charged particles that surround the nucleus
Located in discrete energy levels called shells
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5. The Composition of Minerals
Atomic structure
Atomic number – number of protons in the atom
Atomic weight – approximately the total number of protons and neutrons in the nucleus
Valence electrons – outer most electrons in the shell
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6. The Composition of Minerals
Bonding
Chemical bonds – strong attractive force forms compounds
Ionic bonds – attraction of oppositely charged ions producing electrically neutral compound
Covalent bonds – bonds that share electrons
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7. The Structure of Minerals
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8. The Structure of Minerals
A mineral consists of an ordered array of atoms chemically bonded to form a particular crystalline structure
Polymorph – some elements can join in more than one geometric arrangement
Chemical composition stays the same
Physical properties differ
Example: diamond and graphite
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9. Diamond and graphite are polymorphs of carbon.
The Structure of Minerals
Diamond and graphite are polymorphs of carbon.
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10. Physical Properties of Minerals
Crystal habit (shape)
External expression of the orderly internal arrangement of atoms
Crystal growth is often interrupted because of competition for space and rapid loss of heat
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11. Physical Properties of Minerals
Lustre
Appearance of a mineral in reflected light
Two basic categories
Metallic
Nonmetallic
Other terms, such as vitreous, silky, or earthy, are used to further describe nonmetallic lustre
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12. Physical Properties of Minerals
Colour
Often obvious (yellow, pink etc) but not diagnostic if used for ID alone.
Slight impurities can produce strong colour variations.
Example: Quartz – can be clear, white, rose, smoky, purple etc.
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13. Quartz (SiO2) exhibits a variety of colours as in the purple amethyst.
Physical Properties of Minerals
Quartz (SiO2) exhibits a variety of colours as in the purple amethyst.
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14. Physical Properties of Minerals
Streak
Colour of a mineral in its powdered form when rubbed on an unglazed porcelain tile (streak plate)
Hardness
Resistance of a mineral to abrasion or scratching
All minerals are compared to a standard scale called the Mohs scale of hardness
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15. Physical Properties of Minerals
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16. 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
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17. Physical Properties of Minerals
Fracture
Absence of cleavage when a mineral is broken
Conchoidal fracture – breaks to form smooth curved surfaces like broken glass
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18. Physical Properties of Minerals
Specific gravity
Ratio of the weight of a mineral to the weight of an equal volume of water
Average value is approximately between 2.5 and 3
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19. Physical Properties of Minerals
Other properties (“special properties”)
Magnetism
Reaction to hydrochloric acid
Malleability
Double refraction
Taste
Smell
Elasticity
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20. Mineral Classes Nearly 4000 minerals have been identified
Rock-forming minerals
A few common minerals that make up most of the rocks of Earth’s crust
Composed mainly of the 8 elements that make up over 98% of the continental crust
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21. Mineral Classes
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22. Mineral Classes The Silicates Most common mineral group
Basic building block is the silicon-oxygen tetrahedron
Four oxygen ions surrounding a much smaller silicon ion to form a more complex ion
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23. Mineral Groups More complex Silicate structures
Tetrahedra are linked together to form various structures including:
Single chains
Double chains
Sheet structures
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24. Common Silicate Minerals
Ferromagnesian (dark) silicates
Olivine group
Pyroxenes – includes augite
Amphiboles
Biotite
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25. Common Silicate Minerals
Nonferromagnesian (light) silicates
Mica Group
Muscovite is the common light coloured mica
Feldspar
Orthoclase (potassium feldspar)
Plagioclase
Quartz
Clay
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26. Mineral Classes Important nonsilicate minerals
Several major groups exist including
Oxides
Hydroxides
Sulphides
Sulphates
Native Elements
Halides
Carbonates
Phosphates
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27. Mineral Classes
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28. Gemstones
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