Minerals: Building Blocks of Rocks Chapter 2. Based on: Earth Science, 10e

Transcription

1 Minerals: Building Blocks of Rocks Chapter 2 Based on: Earth Science, 10e

2 Minerals: the building blocks of rocks Definition of a mineral Solid Inorganic Natural Crystalline Structure - Possess an orderly internal structure of atoms Have a definite chemical composition Mineraloid - lacks an orderly internal structure

3 Minerals: the building blocks of rocks Rocks are aggregates (mixtures) of minerals Aggregate implies that the minerals are joined in a way that the properties of each mineral are retained Some are composed of nonmineral matter o Obsidian, pumice and coal

4 Elements Composition and structure of minerals Basic building blocks of minerals Over 100 are known Atoms Smallest particles of matter Have all the characteristics of an element

5 Periodic table of the Elements

6 How atoms are constructed Nucleus central part of an atom that contains Protons positive electrical charges Neutrons neutral electrical charges Energy levels, or shells Surround nucleus Contain electrons negative electrical charges

7 Simplified view of the atom

8 How atoms are constructed Atomic number is the number of protons in an atom's nucleus Isotopes Have varying number of neutrons Have different mass numbers the sum of the neutrons plus protons Many isotopes are radioactive and emit energy and particles which power Earth s interior movements

9 How atoms are constructed

10 Atomic Bonding Bonding of atoms Forms a compound with two or more elements Ions are atoms that gain or lose electrons A compound is a substance consisting of two or more elements chemically combined in specific proportions. Compounds form when atoms are more stable in a combined form.

11 Atomic Bonding Types of Chemical bonds Ionic Bonds form between positive and negatively charged ions (NaCl). Rigid solids with high melting points. Covalent bonds form when atoms share electrons (SiO 2 & H 2 O). Low melting and boiling points. Metallic bonds bonds formed when electrons are shared by metal ions. Sharing of the electron pool gives metals their characteristic properties.

12 Atomic Bonding The properties of a chemical compound are dramatically different from the properties of the elements composing it. Cl green, poisonous gas Na soft, silvery metal that severely reacts with water

13 Minerals How minerals form 4 major processes by which minerals form. o Crystallization by magma o Precipitation o Changes in pressure & temperature o Formation by hydrothermal solutions

14 Minerals Physical properties of minerals Crystal form - The external expression of a mineral s internal orderly arrangement of atoms Luster - Appearance or quality of light reflected from the surface of a mineral Metallic appearance of a metal Nonmetallic vitreous (glassy), pearly, silky, resinous, earthy (dull)

15 Minerals Color - An obvious, yet, unreliable property o Slight impurities can cause a variety of colors Streak - Color of a mineral in its powdered form o A more reliable indicator of color o Determined by using a streak plate o Metallic minerals generally have a dense, dark streak

16 Minerals Hardness - A measure of the resistance of a mineral to abrasion or scratching Mohs Scale o Ranks minerals from 1 10 o Fingernail = 2.5 o Cu penny = 3.5 o Glass, Steel = 5.5

17 The mineral quartz often exhibits good crystal form

18 Pyrite (fool s gold) displays metallic luster

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20 Minerals Cleavage - The tendency of a mineral to cleave, or break, along planes of weak bonding Kleiben = carve Not all minerals have definite planes of weak bonding Those with cleavage can be identified by the distinctive smooth surfaces that are produced when the mineral is broken When minerals break evenly in more than one direction, cleavage is described by the number of planes exhibited and the angles at which they meet

21 Three examples of perfect cleavage fluorite, halite, and calcite

22 Minerals Physical properties of minerals Fracture - Occurs when minerals that do not exhibit cleavage break o Conchoidal fracture smooth curved surfaces o Most fracture irregularly

23 Conchoidal fracture

24 Minerals Specific gravity - Compares the weight of a mineral to the weight of an equal volume of water Heft Usually between 2.5 & 3 Some metallic minerals are higher Galena 7.5 Pure 24k Gold 20

25 Minerals Other properties Taste Smell Elasticity Malleability

26 Minerals Physical properties of minerals Other properties Feel Magnetism Double Refraction Reaction to hydrochloric acid

27 Minerals A few dozen minerals are called the rockforming minerals The eight elements that compose most rockforming minerals are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg) Most abundant atoms in Earth's crust are oxygen (46.6% by weight) and silicon (27.7% by weight)

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29 Minerals Mineral groups Rock-forming silicates Most common mineral group Contain the silicon-oxygen tetrahedron Four oxygen atoms surrounding a much smaller silicon atom Combines with other atoms to form the various silicate structures

30 The silicate (SiO 4 ) -4 molecule

31 Common silicate minerals

32 Minerals Mineral groups Rock-forming silicates Groups based upon tetrahedral arrangement Olivine independent tetrahedra Pyroxene group tetrahedra are arranged in chains Amphibole group tetrahedra are arranged in double chains

33 Hornblende a member of the amphibole group

34 Minerals Mineral groups Rock-forming silicates Groups based upon tetrahedral arrangement Micas tetrahedra are arranged in sheets Two types of mica are biotite (dark) and muscovite (light) Feldspars - Three-dimensional network of tetrahedra

35 Minerals Mineral groups Rock-forming silicates Groups based upon tetrahedral arrangement Feldspars Two types of feldspar are Orthoclase and Plagioclase Quartz three-dimensional network of tetrahedra

36 Potassium feldspar

37 Plagioclase feldspar

38 Minerals Mineral groups Rock-forming silicates Feldspars are the most plentiful mineral group Crystallize from molten material Nonsilicate minerals Major groups Oxides Sulfides

39 Minerals Mineral groups Nonsilicate minerals Major groups Sulfates Carbonates Native elements

40 Native Copper

41 Minerals Mineral groups Nonsilicate minerals Carbonates A major rock-forming group Found in the rocks limestone and marble Halite and gypsum are found in sedimentary rocks Many have economic value

42 Some common non-silicate minerals

43 Minerals Mineral resources Reserves are already identified deposits Ores are useful metallic minerals that can be mined at a profit Economic factors may change and influence a resource

44 An underground halite (salt) mine

45 The Bingham copper mine in Utah

46 End of Chapter 1