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Minerals What Is a Mineral? • A mineral is a solid, naturally occurring substance that has a specific chemical composition and a highly ordered internal (crystalline) structure. What is a Rock? • A solid, cohesive aggregate of grains of one or more minerals CRYSTAL - A mineral grain displaying the characteristics of its atomic structure. - Over 4300 different kinds of minerals (most due to life!) - differences result from the different elements used and the ways they are bonded Chemistry Review : An ELEMENT is determined by the number of PROTONS (+). IONS - Atoms where the number of ELECTRONS (-) have been added or subtracted. ISOTOPES - Atoms where the number of NEUTRONS have been added or subtracted. The Structure of the Atom • • Atomic number = Number of protons Elements Atomic Mass = Number of protons + neutrons Isotopes Periodic Table of the Elements The Structure of the Atom • • Atomic number = Number of protons Elements Atomic mass = Number of protons + neutrons Isotopes Chemical Bonds – Forces that keep atoms together Bonds are strong when the outermost electron energy levels are complete. # of electrons in outermost energy level Total # of electrons 2 2 8 10 8 18 18 36 18 54 Etc. The Structure of the Atom • The size of atom is determined by electron cloud of the ION Changing Model of the Atom Changing Model of the Atom Changing Model of the Atom Changing Model of the Atom Changing Model of the Atom How Atoms Bond Types of bonding • Ionic • Covalent • Metallic • Intermolecular Figure 2-7 Atoms gain or lose electrons, becoming negatively charged ions or positively charged ions that attract each other. How Atoms Bond IONIC BOND Ex: Halite (salt) Q: Which is Na? Cl? How Atoms Bond Types of bonding • Ionic • Covalent • Metallic • Intermolecular Sharing of electrons between similar atoms – strongest type of bond How Atoms Bond Types of bonding • Ionic • Covalent • Metallic • Intermolecular Electrons move continually among close-packed nuclei. How Atoms Bond Types of bonding • Ionic • Covalent • Metallic • Intermolecular Weak attraction between molecules due to an uneven distribution of electrons – van der Waals bond. Mineral Stability • Ion charges must sum to ZERO • Ion sizes must be compatible (electron cloud) Mineral Stability Mineral Stability Mineral Stability • Temperature and pressure play defining roles in establishing stability of mineral Mineral Stability • Why are there different forms of ice at different temperatures and pressures? Mineral Stability • Why are there different forms of ice at different temperatures and pressures? • Because the ion sizes change, relative to each other, at different T & P, so the ideal packing changes. Mineral Stability • How might stishovite occur naturally? Mineral Stability • How might stishovite occur naturally? • Meteorites! Minerals are clues to the past! Mineral Stability • How might stishovite occur naturally? • Meteorites! • Why are they still at the surface? Minerals are clues to the past! Mineral Stability • How might stishovite occur naturally? • Meteorites! • Why are they still at the surface? • Metastability (too cold to change back) Minerals are clues to the past! Diamonds only form naturally more than about 150 km beneath the surface. They are unstable at the surface – they will burn in a fire. Mineral Composition Rock-Forming Minerals A. Silicates – e.g., quartz (SiO2), orthoclase (KAlSi3O8) B. Non-silicate mineral groups – Carbonates - e.g., calcite (CaCO3), dolomite (MgCa(CO3)2) – Oxides - e.g., hematite (Fe2O3), magnetite (Fe3O4) – Sulfides - e.g., pyrite (FeS2), galena (PbS) – Sulfates - e.g., gypsum (CaSO4) – Natives - e.g., gold (Au), silver (Ag), diamond (C), platinum (Pt) Silicates Make up 90% by weight of Earth’s crust • Si and O are the two most abundant elements in the Earth’s crust (differentiation). • Small silicon ions fit snugly in the niches among large closely packed oxygen ions. Silica Tetrahedron: Slightly changing the different elements that combine with silica greatly changes the mineral that results, or the characteristics of the mineral. Ex/ Different forms of quartz Types of Silicates • • • • • Independent tetrahedra Single chains Double chains Sheets Framework Example: Olivine Types of Silicates • • • • • Independent tetrahedra Single chains Double chains Sheets Framework Example: Pyroxene Types of Silicates • • • • • Independent tetrahedra Single chains Double chains Sheets Framework Example: Amphibole Types of Silicates • • • • • Independent tetrahedra Single chains Double chains Sheets Framework Example: Muscovite Types of Silicates • • • • • Independent tetrahedra Single chains Double chains Sheets Framework Example: Quartz Visit the EPS Mineral Collection Only did up to here on 9/16 (it took an hour), to leave a halfhour for more planetary stuff Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests A mineral’s chemical composition and crystal structure give it a unique combination of chemical and physical properties we can use to identify it. Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Figure 2-20 Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Stibnite Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests Figure 20-22 Identifying Minerals • • • • • • • • • • • Color Luster Streak Hardness Cleavage Fracture Smell Taste Crystal form Density Laboratory tests EPS Electron Microprobe Fluorescent lighting spectrum peaks Fluorescent lighting spectrum peaks Peak number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Wavelength of peak (nm) 405.4 436.6 487.7 542.4 546.5 577.7 580.2 584.0 587.6 593.4 599.7 611.6 625.7 631.1 650.8 662.6 687.7 693.7 707 and 709 712.3 760.0 811.0 Species producing peak mercury mercury terbium terbium mercury terbium mercury or terbium terbium from Tb3+ or europium in Eu+3 europium in Eu+3 europium in Eu+3 europium in Eu+3 europium in Eu+3 terbium from Tb3+ europium in Eu+3 europium in Eu+3 europium in Eu+3 europium in Eu+3 europium in Eu+3 europium in Eu+3 europium in Eu+3 argon argon