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
The Nucleus Protons Positive electrical charge The number of protons in the nucleus determines the atomic number
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
Electrons Electrons form clouds around nucleus Negative electrical charge Electrons = protons in electrically neutral atom Variations in the number of electrons produce ions
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
Fig. 3.3 Periodic Table of the Elements
Isotopes Number of protons constant in a given atom Number of neutrons vary Atomic mass varies Isotopes may be stable or radioactive 56 57 58 Fe Fe Fe 26 26 26
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
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
Fig 3.4A Ionic Bonding
Fig 3.4B Covalent Bonding
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.
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
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
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
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
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
Fig. 3.9 A & D Cleavage Planes
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
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
Hematite Colors & Streak
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
Physical Properties Magnetism Characteristic of only a few minerals Iron bearing minerals Magnetite An important property of rocks in geophysical investigations of the Earth
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.
Fig 3.13 Crystal Growth in a Confined Space
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
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%)
Fig 3.18 Silica Tetrahedron
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
Fig 3.19 Silicate Structures
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
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
Feldspars Most abundant mineral in crust, approx 50 % 2 dir. cleavage at rt angles, pearly/waxy luster Hardness: 6 Density: 2.6-2.7 g/cc Striations on cleavage planes Common in igneous and metamorphic rks
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
Micas Biotite, muscovite most common Break into thin, elastic, translucent sheets Perfect 1 dimensional cleavage Hardness: 2-3 Density: 2.8 3.0 g/cc Muscovite lighter, lower density Biotite darker, higher density, tech. mafic
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
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
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
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
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
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.
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
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
End of Chapter 3