The Nucleus. Protons. Positive electrical charge The number of protons in the nucleus determines the atomic number

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2 Matter Atoms The smallest unit of an element that retain its properties Small nucleus surrounded by a cloud of electrons The nucleus contains protons and neutrons

3 The Nucleus Protons Positive electrical charge The number of protons in the nucleus determines the atomic number

4 The Nucleus Neutrons Electrically neutral - no charge The number of neutrons + protons equals the atomic mass The number of neutrons in the nucleus of a given element may vary producing isotopes

5 Electrons Electrons form clouds around nucleus Negative electrical charge Electrons = protons in electrically neutral atom Variations in the number of electrons produce ions

6 Ions Atoms may gain or lose electrons Loss of electrons makes a positively charged ion - cation Gaining electrons makes a negatively charged ion - anion Oppositely charged ions may attract one another

7 Fig. 3.3 Periodic Table of the Elements

8 Isotopes Number of protons constant in a given atom Number of neutrons vary Atomic mass varies Isotopes may be stable or radioactive Fe Fe Fe

9 Bonding Atoms are stable when their outermost electron shell is filled i.e. when their electron structure is like a noble gas Types of bonds: Ionic Covalent Metallic

10 Ionic bonds Bonding Formed between ions of opposite charge (electrons of an atom are lost or gained) Covalent bonds Atoms share electrons to achieve noble gas structure Metallic bonds Outer electrons are mobile Electrical conductivity

11 Fig 3.4A Ionic Bonding

12 Fig 3.4B Covalent Bonding

13 The Nature of Minerals Mineral Definition: A naturally occurring inorganic solid that has an exact chemical composition with an orderly internal arrangement of atoms generally formed by inorganic processes.

14 Minerals Naturally occurring inorganic solid Must be solid Ice vs. water Must be formed by a natural process Natural vs. synthetic diamonds Must be an inorganic compound Coal is not a mineral

15 Minerals Internal structure Repetitive geometric pattern of atoms Expressed in physical properties Interfacial angles Cleavage Polymorph Minerals with the same chemical composition but different internal structure

16 Minerals Exact composition Definite chemical composition expressed as a chemical formula Composition ranges from simple to complex Native copper - Cu Biotite - K(Mg,Fe) 3 AlSi 3 O 10 (OH) 2 Ionic substitution may occur causing small variations in composition

17 Physical Properties Crystal faces & form Growth in unrestricted environment Form reflects symmetry of internal structure Density Ratio of mass to volume Common rock-forming minerals range from 2.6 to 3.4 grams/cm 3

18 Physical Properties Cleavage Breakage along parallel planes of weakness Related to internal structure -weaker bonds May occur in 1 or more planes Fracture is uneven breakage - no natural planes of weakness

19 Fig. 3.9 A & D Cleavage Planes

20 Physical Properties Hardness Resistance to abrasion Strength of atomic bonds holding solid together Mohs hardness scale Arbitrary relative numbers assigned to 10 common minerals Scale is not linear

21 Physical Properties Color Most obvious property Not diagnostic for ID purposes Variations due to trace elements Streak Color of mineral in powder form when rubbed against unglazed porcelain Diagnostic property

22 Hematite Colors & Streak

23 Physical Properties Luster The appearance of reflected light Influenced by the type of bonding in the mineral Metallic luster Shines like metal Non-metallic Widely ranging from bright to dull

24 Physical Properties Magnetism Characteristic of only a few minerals Iron bearing minerals Magnetite An important property of rocks in geophysical investigations of the Earth

25 Growth & Destruction of Minerals Crystallization: T & P are ideal and proper atoms/ions present Addition of atoms to the crystal face Follows internal structure Different rates fast elongated xstal Ideal crystal forms are produced by growth in unrestricted space In restricted space, crystals grow to fill the space. Most common situation.

26 Fig 3.13 Crystal Growth in a Confined Space

27 Growth & Destruction of Minerals Mineral destruction Melting (heating) or dissolution Removal of atoms from crystal faces as matter goes from solid to liquid Recrystallization Rearrangement of the internal structure of a mineral by changing pressure and temperature Solid state reaction

28 Silicate Minerals Most common minerals on Earth Comprise 95% of the volume of the crust All silicate minerals are based on the silica tetrahedron (pyramid) basic building block SiO 4-4 Most abundant elements in crust by weight: O (47%) and Si (28%)

29 Fig 3.18 Silica Tetrahedron

30 Silicate Minerals Five fundamental configurations of silica tetrahedron: Isolated tetrahedron ex. Olivine Single chains ex. Pyroxenes Double chains ex. Amphiboles 2-D sheet ex. Micas, clays 3-D frameworks ex. Feldspars, quartz

31 Fig 3.19 Silicate Structures

32 Rock-Forming Minerals About 20 common minerals make up most rocks in crust & upper mantle Silicates dominate Quartz, feldspars, micas, olivine, pyroxene, amphiboles, clays Non silicates Carbonates are common Evaporite minerals

33 Felsic Silicate Minerals Rich in Si and Al Rel. low densities and low xstal. temps Major constituents of continental crust Quartz Feldspars Potassium feldspar Plagioclase feldspar Mica - muscovite

34 Feldspars Most abundant mineral in crust, approx 50 % 2 dir. cleavage at rt angles, pearly/waxy luster Hardness: 6 Density: g/cc Striations on cleavage planes Common in igneous and metamorphic rks

35 Quartz Very common; very stable mech. & chem. thus hard to break down No cleavage; glassy, conchoidal fracture Hardness: 7 Density: 2.7 g/cc When crystals present 6 sided, elongated Very common in igneous, sed., and meta. rks

36 Micas Biotite, muscovite most common Break into thin, elastic, translucent sheets Perfect 1 dimensional cleavage Hardness: 2-3 Density: g/cc Muscovite lighter, lower density Biotite darker, higher density, tech. mafic

37 Mafic Silicate Minerals Rich in Fe and Mg Rel. high densities and high xstal. temps Major constituents of oceanic crust & upper mantle Olivine Pyroxenes Amphiboles Mica - biotite

38 Olivine One of few minerals where olive green, glassy color is diagnostic hardness: 6.5 Forms at high temps density: 3.4 g/cc Gemstone: peridot (August birthstone) Major constituent of upper mantle

39 Pyroxenes Crystallize at high temps Dark green to black 2 directions cleavage at right angles Hardness: 6 density: 3.3 g/cc Crystals are short and stubby Common in igneous and meta. rks

40 Amphiboles Green to black 2 direction of cleavage NOT at right angles (60 and 120) Hardness: 5 6 density: 3.2 g/cc Crystals are commonly elongate Common in igneous and meta. rks

41 Clay Minerals 2-D sheet silicates similar to mica Products of chemical weathering near the Earth s surface when air/water break down other silicates Usually microscopic crystals Kaolinite

42 SEM photograph of clay minerals: authigenic chlorite flake from the Watahomigi Formation in Andrus Canyon, Supai Group, Grand Canyon; x 20,900. Figure 05-D, U.S. Geological Survey Professional Paper 1173.

43 Nonsilicate Minerals Usually form at low temp & press at/ near Earth s surface Carbonates Calcite - Ca CO 3 Direct ppc from seawater or as shells; lmst, marble Fizzes in dilute HCl acid 3 directions cleavage NOT at rt angles Hardness: 3 density: 2.7 g/cc Dolomite - CaMg(CO 3 ) 2 Slightly more dense; fizzes in powdered form only

44 Nonsilicate minerals cont d Evaporite Minerals seawater/saline lakes Gypsum - CaSO 4-2H 2 O Glassy or silky/waxy luster Perfect cleavage in 1 direction Hardness: 2 density: 2.3 g/cc Halite NaCl Oxides Cleaves at right angles in 3 directions Hematite, Magnetite

45 End of Chapter 3