Minerals

Minerals - Essentials of Geology Essentials Chapter 3 Do...

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Unformatted text preview: Essentials of Geology Essentials Chapter 3 Do you know what you are looking at? Patterns in Nature: Minerals Minerals Minerals are the “building blocks” of rocks/ Earth Minerals More than 4,000 are known Dozens of new minerals are discovered annually Human interest in minerals spans millenia Human Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Minerals Developed societies depend on mineral resources Metals – Iron, copper, lead, zinc, nickel, aluminum, etc Metals Non-metals – Gypsum, limestone, aggregate, clay Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Minerals Economically important – Drive world economies Historically important – Dictated human history Iron Copper Gold Diamonds Gems Figure 3.2a Figure 3.1 Figure 3.2b Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Mineral Definition Geologic definition of a mineral is specialized: Naturally occurring Solid Definite chemical Definite composition Ordered atomic Ordered arrangement arrangement Mostly inorganic A mineraloid exhibits some of these properties mineraloid Doesn’t include “minerals” in the nutritional sense Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Rocks Most rocks are earth materials made from minerals Most rocks contain more than one kind of mineral Example: Granite K-feldspar – Pink Quartz – Gray Biotite – Black Some are monomineralic Limestone (Calcite) Rock salt (Halite) Glacial ice Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystalline Structure Atoms in a mineral are specifically ordered A solid with disordered atoms is called a glass solid glass Crystalline structure is based on atomic patterns Crystalline Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystals Rare minerals displaying flat external faces Crystal faces form best in open cavities Crystals are often prized mineral specimens Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystal Lattice Ordered atoms in crystals form a 3-D lattice Lattices are patterns that repeat in three dimensions Lattices This internal pattern controls most mineral properties This Crystal shape Symmetry Symmetry Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystals Constancy of interfacial angles Different samples of the same mineral will have the same Different crystal faces crystal Adjacent faces are always Adjacent oriented at the same angle oriented Crystal faces reflect the Crystal internal atomic order internal Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals We are now interrupting the program We for some shaking experience … for Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Table Salt Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Atomic Bonding Lattice atoms are held in place by atomic bonds Bond characteristics also govern mineral properties Bond Models depict atoms, bonds, and lattices Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Polymorphs Minerals with the same composition; different structure Diamond and graphite are carbon polymorphs Diamond polymorphs Polymorphs reveal the importance of bond type Diamond – Strong covalent bonds; hardest mineral Graphite – Weak Van-der-Waals bonds; very soft mineral Diamond Graphite Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystal Growth Crystals grow as atoms attach to mineral surfaces Crystals Growth starts from a central seed crystal Growth expands outward as atoms accumulate Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystal Growth Outward crystal growth fills available space Resulting crystal shape is governed by surroundings Open space – Good crystal faces grow Confined space – No crystal faces Crystals grow by… Crystals Solidification from a melt Precipitation from solution Solid-state diffusion Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Fig. 3.7b Time 1 Crystals growing without interference are euhedral Time 2 When growing crystals interfere, they become anhedral Essentials of Geology, 3rd edition, by Stephen Marshak Crystals grown in a confined space are anhedral Chapter 3: Patterns in Nature: Minerals Mineral Physical Properties Characteristics determined by your five senses Used to ID minerals Properties depend upon… Chemical composition Crystal structure Some are diagnostic Pyrite Example: Pyrite (FeS2) Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brassy color, sulfur smell when crushed, erroneously mistaken for gold (fool’s gold). erroneously Minerals have unique sets of physical properties Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Mineral Physical Properties Common properties of Common minerals are... minerals Crystal form Crystal habit Luster Color Streak Hardness Cleavage Fracture Specific gravity Needle-like crystal habit Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Mineral Physical Properties Less common physical properties are... Taste Smell Feel Elasticity Magnetism Effervescence Diaphaneity Piezoelectricity Pyroelectricity Refractive index Malleability Ductility Sectility Essentials of Geology, 3rd edition, by Stephen Marshak Magnetite crystals on a large magnet. Calcite effervesces with acid Chapter 3: Patterns in Nature: Minerals Color – Do not rely on it! Color is diagnostic for some minerals Color some Azurite is always blue Some minerals may exhibit a broad color range >>> Color varieties often reflect trace impurities Quartz (Clear, white, yellow, pink, purple, gray, etc) Olivine can be light olive green OR almost black Olivine OR Quartz – Many colors Essentials of Geology, 3rd edition, by Stephen Marshak Malachite – Always green Chapter 3: Patterns in Nature: Minerals Streak: more diagnostic than Color Mineral color crushed on an unglazed porcelain plate Streak is often a useful diagnostic property Congruent streak – Streak color the same as the mineral Congruent Magnetite – Black mineral; black streak Incongruent streak – Streak color differs from the mineral Chromite – Black mineral; greenish-brown streak Hematite – Red-brown streak Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Luster The way a mineral surface scatters light Two subdivisions Two Metallic – Looks like a metal Nonmetallic: Adamantine (brilliant) Vitreous (glassy) Satiny Silky Resinous Pearly Earthy (dull) Earthy Quartz – Vitreous luster Satin spar Gypsum – Satiny luster Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Hardness Scratching resistance of a mineral Scratching Hardness compared to the Mohs hardness scale Talc, Graphite. Gypsum Calcite Fluorite Apatite Orthoclase Orthoclase Quartz Topaz Corundum Diamond Fingernail 2.5 Copper Penny 3.5 Glass - Steel 5.5 Steel File 6.5 Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Specific Gravity Related to density (mass per volume) Mineral weight over weight of equal water volume Specific gravity is “heft”– How heavy it feels Pyrite – Heavy (SG 5.0) Feldspar – Light (SG 2.6) Pyrite “feels” heavier than feldspar Potassium Feldspar Pyrite Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Crystal Habit Crystal habit is the ideal shape of crystal faces Ideal faces require ideal growth conditions Ideal Many descriptive terms are used to characterize habit Many Cubes Dodecahedra Octahedra Compound Forms Essentials of Geology, 3rd edition, by Stephen Marshak Blades Rhombohedra Hexagonal Prisms Tetragonal Prisms Chapter 3: Patterns in Nature: Minerals Crystal Form Minerals vary in crystal face development Euhedral – Good crystal faces; grown in open cavity Euhedral Good Anhedral – No crystal faces; grown in tight space Anhedral Subhedral – Between the two Subhedral Between Face development indicates growth history Anhedral crystals common; euhedral less so Anhedral Amethyst Geode Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Cleavage Tendency to break along planes of lattice weakness Cleavage produces flat, shiny surfaces Described by the number of planes and their angles Sometimes mistaken for crystal habit Sometimes Cleavage is through going; often forms parallel “steps” Habit is only on external faces Habit 1, 2, 3, 4, and 6 cleavages possible 1, Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Cleavage Cleavage Examples of Cleavage: 1 direction Muscovite Mica 2 directions at ~ 90º Potassium Feldspar 2 directions NOT at 90º Amphibole Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Cleavage Cleavage Examples of Cleavage: Three directions at 90º Halite Three directions NOT at 90º Calcite Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Fracture Some minerals lack planes of lattice weakness; due to equal molecular bonds in all directions These minerals don’t cleave; they exhibit fracture Example: Quartz displays conchoidal fracture Example: conchoidal Shaped like the inside of a clam shell Shaped Breaks along smooth, curved surfaces Produces extremely sharp edges Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Mineral Compositions Only about 50 minerals are abundant. Only 98% of crustal mineral mass is from eight elements. Oxygen Oxygen Silicon Aluminum Aluminum Iron Calcium Calcium Sodium Sodium Potassium Potassium Magnesium Magnesium All others All O Si Al Al Fe Ca Ca Na Na K Mg Mg Essentials of Geology, 3rd edition, by Stephen Marshak 46.6% 27.7% 8.1% 5.0% 3.6% 2.8% 2.6% 2.1% 1.5% 74.3% of crustal minerals !!! 74.3% of crustal minerals !!! Chapter 3: Patterns in Nature: Minerals Mineral Classes Minerals are classified based upon the dominant anion. Silicates Silicates Oxides O2SulfidesSSulfatesSO42- SiO24SiO Chief rock-forming minerals Chief Magnetite, Hematite Magnetite, Pyrite, Galena Pyrite, Gypsum Gypsum Halides Halides Carbonates Cl- or FCl CO32- Fluorite, Halite Fluorite, Calcite, Dolomite Calcite, Native elem. Cu, Au, C Copper, Gold, Graphite Malachite (Carbonate) Essentials of Geology, 3rd edition, by Stephen Marshak Fluorite (Halide) Native Copper Chapter 3: Patterns in Nature: Minerals Silicate Minerals Silicates are know as “the rock-forming minerals” Silicates They dominate Earth’s crust Oxygen and silicon… Oxygen Make up 94.7% of crustal volume, and... Make volume 74.3% of crustal mass 74.3% mass Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Silly Kate! The anionic unit is the silica tetrahedron 4 oxygen atoms are bonded to 1 silicon atom (SiO44-) Silicon is tiny; oxygen is huge The silica tetrahedron has a net -4 ionic charge The silicate unit can be depicted by… Spheres A ball-and-stick model Polyhedra Polyhedra Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Silicate Minerals Silica tetrahedra link together by sharing oxygens More shared oxygen = lower Si:O ratio; governs… Melting temperature Mineral structure and cations present Mineral Susceptibility to chemical weathering Susceptibility Type of Silicate Structure Formula Si:O Ratio Independent Tetrahedra SiO4 0.25 Double Tetrahedra Si2O7 0.29 Ring Silicates Si6O18 0.33 Single Chains SiO3 0.33 Double Chains Si4O11 0.36 Sheet Silicates Si2O5 0.40 Framework Silicates SiO2 0.50 Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Independent Tetrahedra Tetrahedra share no oxygen atoms; linked by cations Olivine group (mantle!) High-temperature Fe-Mg silicate Small green crystals; no cleavage Garnet group Equant crystals with no cleavage Dodecahedral (12-sided) crystals Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Single-Chain Silicates Single-chain structures bonded with Fe and Mg Pyroxene Group Black-to-green color Black-to-green Two distinctive cleavages at nearly 90° Stubby crystals Augite is the most common pyroxene Pyroxene Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Double-Chain Silicates Double chain of silica tetrahedra bonded together Double Contain a variety of cations Amphibole group Amphibole - two cleavages; elongate crystals Hornblende Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Sheet Silicates Two dimensional sheets of linked tetrahedra Characterized by one direction of perfect cleavage Mica group – Biotite (dark) and Muscovite (light) Clay mineral group – Feldspar-weathering residue; tiny Clay Muscovite Mica Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Framework Silicates All four oxygen atoms in the silica tetrahedra are shared Form the most common minerals of the Earth’s crust Feldspar group – Plagioclase and potassium feldspar Silica (Quartz) group – Contains only Si and O Silica Potassium Feldspar Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Gems Minerals with special value Minerals Rarity Beauty Color Hardness Interaction with light Aquamarine Beryl High refractive index Watermelon Tourmaline Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Gems Gems are cut and polished to be used in jewelry Facets are ground onto a gemstone by a machine Facets are not natural crystal faces Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals Diamonds are cool! Diamonds originate under extremely high pressure ~ 150 km deep (upper mantle) Pure carbon is compressed into the diamond structure Rifting causes deep mantle rock to move upward Diamonds are found in kimberlite pipes Diamonds pipes Essentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: Minerals ...
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