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Introduction to Minerals Questions… • Why learn about minerals? – They are the source of great wealth and beauty. – Minerals provide clues about the geologic past. • How could knowing about minerals assist you in buying a home? – Some minerals are very unstable when exposed to water and air. • How do minerals form? DEFINITION OF A MINERAL •naturally occurring •inorganic •solid •orderly internal structure (crystal) •with a definite chemical composition. (can vary within a specified range) MINERAL CLASSIFICATION •Minerals are classified based on their: – Physical properties –Chemical composition – Crystal Structure ATOMIC STRUCTURE OF MATTER •Elements –Form of matter than cannot be reduced to a simpler form by heat, cold, or chemical reactions. •Atoms – basic form of an element. –Protons – positive charge particle in the nucleus –Neutrons – neutrally charged particle in the nucleus –Electrons – negatively charged particle outside the nucleus. CHEMICAL ELEMENTS pure substances that cannot be decomposed by ordinary means to other substances. Aluminum Sodium Bromine Chemical Symbols Atoms Electron energy levels CHEMICAL COMPOUNDS are composed of atoms and so can be decomposed to those atoms. The red compound is composed of • nickel (Ni) (silver) • carbon (C) (black) • hydrogen (H) (white) • oxygen (O) (red) • nitrogen (N) (blue) Compounds – composed of 2 or more elements in a fixed ratio – properties differ from those of individual elements – EX: table salt (NaCl) A MOLECULE is the smallest unit of a compound that retains the chemical characteristics of the compound. Composition of molecules is given by a MOLECULAR FORMULA H2O C8H10N4O2 - caffeine Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons (All atom aspire to be “NOBLE”) C would like to Gain 4 electrons N would like to Gain 3 electrons O would like to Gain 2 electrons 1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions. 2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2) Double and even triple bonds are commonly observed for C, N, P, O, and S H2CO SO3 C2F4 - water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen. Ice (water crystals) takes up more space than liquid water because of hydrogen bonding Metallic Bonding- electrons flow freely around metal atoms The balance of energy • Atoms have a desire to have their outermost energy level full of electrons, otherwise a “lone” electron may be lost to other elements or may be paired with a “lone” electron from another atom. • Think of a teeter-totter with only one person, or one with an unbalanced number of participants. Periodic Table http://www.webelements.com/webelements/scholar/index.html Atomic number – Number of protons and electrons Periodic Table Tendency to lose outer electrons in order to become more “stable.” Periodic Table Tendency to gain outer electrons in order to become more “stable.” Periodic Table Transition elements – also known as the heavy metals Tend to share electrons to become stable Periodic Table Inert gases, which are already stable and don’t need additional electrons MINERAL COMPOSITION •Minerals are made of different ions bonded together (gain, lose, or share electrons) •Ions are charged atoms. Figure 2.4, Page 28 Chemical Bonding of Sodium (Na) and Chlorine (Cl) Diagrammatic arrangement of sodium and chlorine ions in table salt Sharing of electrons between two chlorine ions to for a molecule of chlorine gas (Cl2) Stacking ions to form different crystal structures From atomic theory to a real crystal In Minerals (Crystals) Physical Arrangement is more important than Chemical Composition BONDING IN MINERALS •Ionic bonding opposite charges attract (gain or lose electrons) •Covalent bonding –ions share electrons •Metallic bonding –free moving electrons Atomic Structure of Minerals •Arrangement of atoms or ions in an orderly, repeating three-dimensional array. (Gases) Atomic Structure of Minerals •External shape is a reflection of the internal crystal structure. halite diamond staurolite quartz W. W. Norton garnet stibnite calcite kyanite Atomic Structure of Minerals • Polymorphism - diamond and graphite Two Minerals from a Single Element Diamond and Graphite Atomic structure can lead to symmetry in some minerals Atomic structure can lead to symmetry in some minerals Halite What is the difference between a mineral and a rock? • Rocks are made up of more than one mineral – Example: Granite contains the minerals quartz, plagioclase, and mica. • Minerals contain a specific chemical composition – Example: Quartz - SiO2 Growth and Destruction of Minerals • Growth occurs through crystallization, which is the addition of atoms to a crystal face, in a liquid environment. – Requires: (1) sufficient quantity of the ions, (2) proper temperature and pressure (space). • Growth generally occurs in a confined space. Thus, external shape may not reflect internal structure. ROCK-FORMING MINERALS •Silicates •Carbonates •Sulfates •Halides Silicates •Silica Tetrahedron –1 silicon ion bonded to 4 oxygen ions •Silicon is positively charged (+4) •Oxygen is negatively charged (-2) •Net charge on tetrahedron : -4 •(SiO44-) More details on the Silicates • Make up 95% of the Earth’s Volume • Basic structural shape is the tetrahedron, which defines the mineral groups: – – – – – Isolated tetrahedron (olivine) Single chain (pyroxene - augite) Double chain (amphibole) Two-dimensional sheet (micas, clays) Three-dimensional framework (quartz, feldspars) Clay minerals • Form at or near Earth’s surface in the presence of air and water from the breakdown of other silicates • Sheet silicates like the micas. • Very small crystals. • Low density – Example: kaolinite Isolated tetrahedron Isolated Isolated tetrahedron (olivine) -Does not break a certain way Isolated tetrahedron Single Chain Single chain (pyroxene - augite) -Breaks on 2 planes at right angles Isolated tetrahedron Double Chain Double chain (amphibole hornblend) -Breaks on 2 planes at 60° and 120° Isolated tetrahedron Two dimensional sheet Two-dimensional sheet (micas muscovite) -Breaks in 1 plane Isolated tetrahedron Three dimensional framework Three-dimensional framework (quartz, feldspars - orthoclase) -Breaks on 2 planes at 90° MINERAL IDENTIFICATION Color Streak Fracture Habit Specific Gravity Hardness Luster Cleavage Taste Smell Magnetic Effervescence –Mohs Hardness Scale Bowen’s Reaction Series the realationship between temperature and the formation of crystals in magma 1400 oC Olivine Pyroxene Amphibole Biotite Mafic Calcium-rich Plagioclase Sodium-rich Intermediate Orthoclase Muscovite 800 oC Quartz Felsic Crust composition – most common elements Mafic • Minerals rich in iron and magnesium • Representative of high density, high temperature magmas. • Examples: – Olivine, pyroxenes, amphiboles Felsic minerals • Minerals rich in silicon and aluminum. • Representative of low density, low temperature magmas. • Examples: – Feldspars, quartz, micas Mineral Destruction • Minerals can melt under high temperatures, removing of outer atoms - melting • Under high pressures, some minerals melt, while others may partially melt, resulting in same chemical composition, but different crystal structure. • Weathering - physical and chemical breakdown of minerals – Some atoms can be pried loose from the structure by water – dissolving (example: NaCl) Carbonates • Basic structure contains the strong, covalent bonded carbonate ion CO32– Bonds easily (ionic) with metals, such as calcium to form calcium carbonate or calcite (CaCO3) CaCO3 is often precipitated directly from carbonate rich seawater. – Shell organisms capture carbonate and combine it with calcium to form CaCO3. Carbonates #2 • Most common mineral is calcite and found readily in limestone and dolomite rock. • Calcite is relatively soft, 3-4 on Mohs hardness scale, and can dissolve in acids (even mild carbonic acid). – Results in cave formation – Weathering of statues and buildings due to acid rain. • Calcite is one mineral that easily deforms and reforms at the Earth’s surface. Often find calcite crystals in the cracks of rocks • Calcite can be easily mistaken for quartz, but a scratch test can remedy the dilemma. • Dolomite (CaMg(CO3)2 bonds a little more tightly with two carbonate ions, resulting in more resistance to acid destruction. Sulfates • Gypsum (CaSO4 ·2H2O) • Anhydrite (CaSO4) – note the two missing water molecules, hence the “An” in the mineral name. Plaster contains anhydrite. • Barite (BaSO4) is soft and “greasy” feeling. Since it doesn’t burn under intense friction, barite serves as an excellent lubricant for drilling. Halides • Common Salt (NaCl) – Halite • Found in thick layers where ancient seas have since evaporated. Elements as Minerals • • • • • • Sulfur Gold Silver Platinum Diamond Many of these metals are often associated with sulfide minerals and low temperature silicates (e.g. quartz veins). References • The Mineral Gallery (commercial site) – http://mineral.galleries.com/