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Chapter 3: Matter and Minerals (part II). Minerals: the building blocks of rocks Definition of a Mineral: naturally occurring inorganic solid characteristic.

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Presentation on theme: "Chapter 3: Matter and Minerals (part II). Minerals: the building blocks of rocks Definition of a Mineral: naturally occurring inorganic solid characteristic."— Presentation transcript:

1 Chapter 3: Matter and Minerals (part II)

2 Minerals: the building blocks of rocks Definition of a Mineral: naturally occurring inorganic solid characteristic crystalline structure definite chemical composition

3 How do we identify minerals? Physical properties: Color Luster Hardness Crystal shape Cleavage Specific gravity Other

4 Physical Properties of Minerals Color: –Most obvious, but often misleading –Different colors may result from impurities Example: Quartz

5 Physical Properties of Minerals Color: Streak – color of a mineral in powdered form (used for metallic minerals) Obtained by scratching a mineral on a piece of unglazed porcelain. Example: Hematite

6 Physical Properties of Minerals Luster: –How a mineral surface reflects light –Two major types: Metallic luster Non-metallic luster Metallic example: Galena Non-metallic example: Orthoclase

7 Physical Properties of Minerals Hardness: –How easy it is to scratch a mineral –Mohs Scale of Hardness relative scale consists of 10 minerals, ranked 1 (softest) to 10 (hardest)

8 Mohs Scale of Hardness Hardest (10) – Diamond Softest (1) – Talc Common objects: - Fingernail (2.5) - Copper penny (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5)

9 Physical Properties of Minerals Crystal shape (or form): –external expression of a minerals internal atomic structure –planar surfaces are called crystal faces –angles between crystal faces are constant for any particular mineral Quartz Pyrite

10 Physical Properties of Minerals Cleavage vs. Fracture: –The way a mineral breaks –Cleavage: tendency of a mineral to break along planes of weakness –Minerals that do not exhibit cleavage are said to fracture Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.

11 Physical Properties of Minerals Cleavage is described by: –Number of planes –Angles between adjacent planes –These are constant for a particular mineral

12 Physical Properties of Minerals Cleavage (1 direction): Example: mica

13 Physical Properties of Minerals Cleavage (2 directions): orthoclase amphibole

14 Physical Properties of Minerals Cleavage (3 directions): halite calcite

15 Physical Properties of Minerals Cleavage (4 directions): fluorite

16 Physical Properties of Minerals Fracture: –minerals that do not exhibit cleavage are said to fracture –smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture Quartz

17 Physical Properties of Minerals Specific gravity: –weight of a mineral divided by weight of an equal volume of water –metallic minerals tend to have higher specific gravity than non-metallic minerals Galena SG=7.5 Quartz SG=2.67

18 –reaction with hydrochloric acid (calcite fizzes) Physical Properties of Minerals Other properties: –taste (halite tastes salty) –feel (talc feels soapy, graphite feels greasy) –magnetism (magnetite attracts a magnet)

19 Rock-forming minerals –~30 common minerals make up most rocks in Earths crust –Composed mainly of the 8 elements that make up over 98% of the crust Mineral Groups

20 All others: 1.5% Element Abundances Silica (SiO 4 ) 4- SILICATES Common cations that bond with silica anions

21 –Oxides O 2- –Carbonates(CO 3 ) 2- –Sulfides S 2- –Sulfates(SO 4 ) 2- –HalidesCl -, F -, Br - –Native elements(single elements; e.g., Au) Mineral Groups Silicates (most abundant) Non-silicates (~8% of Earths crust):

22 Mineral Groups – Silicates Silicates –Tetrahedron fundamental building block 4 oxygen ions surrounding a much smaller silicon ion Silicon-oxygen tetrahedron (SiO 4 ) 4-

23 Mineral Groups – Silicates Joining Silicate Structures –How tetrahedra may be linked: independent tetrahedra single chains double chains sheets 3-D framework

24 Mineral Groups – Silicates –

25 Olivine Group dark silicates (Fe-Mg) Mineral Groups – Silicates No cleavage ferromagnesian

26 Pyroxene Group Ferromagnesian / dark silicates (Fe-Mg) Mineral Groups – Silicates 2-directions of cleavage (at nearly 90 degrees) Augite

27 Amphibole Group Ferromagnesian / dark silicates (Ca, Fe-Mg) Mineral Groups – Silicates 2-directions of cleavage (not at 90 degrees) Hornblende

28 Mica Group and Clay Minerals light silicates (K, Al) Mineral Groups – Silicates 1-direction of cleavage Muscovite non-ferromagnesian

29 Feldspar Group light silicates (K-Na-Ca, Al) Mineral Groups – Silicates 2-directions of cleavage (at 90 degrees) Orthoclase Plagioclase K-feldspar Ca/Na-feldspar Most common mineral group

30 Quartz light silicates (pure SiO 2 ) Mineral Groups – Silicates no cleavage (conchoidal fracture) hard, resistant to weathering Quartz

31 Mineral Groups Ferromagnesian Silicates (Fe, Mg) Non-ferromagnesian Silicates (K, Na, Ca, Al) Oxides Carbonates Sulfides/sulfates Native elements


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