Minerals and Rocks

Lecture Outline What are minerals? What are minerals? Common rock-forming minerals Common rock-forming minerals Physical properties of minerals Physical properties of minerals Basic rock types Basic rock types The rock cycle The rock cycle

Minerals Natural Natural Solid Solid Atoms arranged in orderly repeating 3D array: crystalline Atoms arranged in orderly repeating 3D array: crystalline Not part of the tissue of an organism Not part of the tissue of an organism Composition fixed or varies within defined limits Composition fixed or varies within defined limits Minerals are the “building blocks” of rock A mineral is a naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition

Large individual crystals (rare) Mass of small grains: each is a crystal, but grown up against each other

Atomic Structure of Minerals NaCl - sodium chloride NaCl - sodium chlorideHalite

Chemical Bonds: Ionic Electrical attraction between ions of opposite charge Electrical attraction between ions of opposite charge Bond strength increases with the electrical charges of the ions Bond strength increases with the electrical charges of the ions Bond strength decreases as the distance between the ions increases Bond strength decreases as the distance between the ions increases Most minerals are this kind of compound Most minerals are this kind of compound

Na + Cl - Ionic Bonding example: halite AnionCation

Covalent Bonds: Electron sharing Electron sharing Generally stronger than ionic bonds (e.g., diamond) Generally stronger than ionic bonds (e.g., diamond)

Crystallization of Minerals Need starting material with atoms that can come together in the proper proportions Need starting material with atoms that can come together in the proper proportions Growth from a liquid or a gas Growth from a liquid or a gas Time and space for crystallization Time and space for crystallization Appropriate temperature and pressure Appropriate temperature and pressure Examples Examples Magma that has cooled below its melting point Magma that has cooled below its melting point Supersaturated solution --> precipitation Supersaturated solution --> precipitation

Crystallization of Minerals Crystals begin as an initial “seed” - a microscopic crystal Crystals begin as an initial “seed” - a microscopic crystal Atoms keep being added in a 3D array, repeating the basic arrangement Atoms keep being added in a 3D array, repeating the basic arrangement Crystal faces are based on the array structure Crystal faces are based on the array structure

Cations and Anions Anions are typically large Anions are typically large Cations are relatively small Cations are relatively small Crystal structure is determined largely by the arrangement of the anions Crystal structure is determined largely by the arrangement of the anions

Common cations and anions Radii given in angstroms; cm

Ions can be compound So far, we’ve talked about individual atomic ions So far, we’ve talked about individual atomic ions Many common minerals are silicates Many common minerals are silicates SiO 4 4- Complex ions act as a single ion in forming crystal structure

Cation Substitution Crystal structure determined by those large anions Crystal structure determined by those large anions Various cations can substitute for each other in many minerals Various cations can substitute for each other in many minerals Same crystal structure Same crystal structure Different chemical composition Different chemical composition

Polymorphs Minerals with the same composition, but different crystal structure. Minerals with the same composition, but different crystal structure.

Common Rock-Forming Minerals Minerals fall into a small number of related “families” based mainly on the anion in them

Silicates Most abundant minerals in the Earth's crust Most abundant minerals in the Earth's crust Silicate ion (tetrahedron), SiO 4 4- Silicate ion (tetrahedron), SiO 4 4- Quartz (SiO 2 ), K-feldspar (KAlSi 3 O 8 ), olivine ((Mg, Fe) 2 SiO 4 ), kaolinite (Al 2 Si 2 O 5 (OH) 4 ) Quartz (SiO 2 ), K-feldspar (KAlSi 3 O 8 ), olivine ((Mg, Fe) 2 SiO 4 ), kaolinite (Al 2 Si 2 O 5 (OH) 4 )

Quartz (SiO 2 )

Silicate structure Most of the most common rocks in the crust are silicates Most of the most common rocks in the crust are silicates Silicate tetrahedra can combine in several ways to form many common minerals Silicate tetrahedra can combine in several ways to form many common minerals Typical cations: Typical cations: K +, Ca +, Na +, Mg 2+, Al 3+, Fe 2+

Different numbers of oxygen ions are shared among tetrahedra

Carbonates Cations with carbonate ion (CO 3 2- ) Cations with carbonate ion (CO 3 2- ) Calcite (CaCO 3 ), dolomite (CaMg(CO 3 ) 2 ), siderite (FeCO 3 ), smithsonite (ZnCO 3 ) Calcite (CaCO 3 ), dolomite (CaMg(CO 3 ) 2 ), siderite (FeCO 3 ), smithsonite (ZnCO 3 ) Make up many common rocks including limestone and marble Make up many common rocks including limestone and marble Very important for CCS! Very important for CCS!

Calcite (CaCO 3 )

CaCO 3 + 2H + = Ca 2+ + CO 2 + H 2 O

Smithsonite (ZnCO 3 )

Oxides Compounds of metallic cations and oxygen Compounds of metallic cations and oxygen Important for many metal ores needed to make things (e.g., iron, chromium, titanium) Important for many metal ores needed to make things (e.g., iron, chromium, titanium) Ores are economically useful (i.e., possible to mine) mineral deposits Ores are economically useful (i.e., possible to mine) mineral deposits

Hematite (Fe 2 O 3 )

Sulfides Metallic cations with sulfide (S 2- ) ion Metallic cations with sulfide (S 2- ) ion Important for ores of copper, zinc, nickel, lead, iron Important for ores of copper, zinc, nickel, lead, iron Pyrite (FeS 2 ), galena (PbS) Pyrite (FeS 2 ), galena (PbS)

Galena (PbS)

Sulfates Minerals with sulfate ion (SO 4 2- ) Minerals with sulfate ion (SO 4 2- ) Gypsum (CaSO 4. H 2 O), anhydrite (CaSO 4 ) Gypsum (CaSO 4. H 2 O), anhydrite (CaSO 4 )

Gypsum

Cave of the Crystals 1,000 feet depth in the silver and lead Naica Mine 150 degrees, with 100 % humidity 4-ft diameter columns 50 ft length Gypsum

Identification of Minerals Chemical composition (microprobes and wet chemical methods) Chemical composition (microprobes and wet chemical methods) Crystal structure (X-ray diffraction) Crystal structure (X-ray diffraction) Physical properties Physical properties

Physical properties Hardness Hardness

Physical properties Hardness Hardness Cleavage: tendency of minerals to break along flat planar surfaces into geometries that are determined by their crystal structure Cleavage: tendency of minerals to break along flat planar surfaces into geometries that are determined by their crystal structure

Cleavage in mica

Cleavage in calcite

Halite (NaCl)

Physical properties Hardness Hardness Cleavage Cleavage Fracture: tendency to break along other surfaces (not cleavage planes) Fracture: tendency to break along other surfaces (not cleavage planes)

Conchoidal fractures

Physical properties Hardness Hardness Cleavage Cleavage Fracture Fracture Luster (metallic, vitreous, resinous, earthy, etc.) Luster (metallic, vitreous, resinous, earthy, etc.) Color (often a poor indicator; streak color is better) Color (often a poor indicator; streak color is better) Specific gravity Specific gravity Crystal habit (shape) Crystal habit (shape)

Rocks An aggregate of one or more minerals; or a body of undifferentiated mineral matter (e.g., obsidian); or of solid organic matter (e.g., coal) More than one crystal More than one crystal Volcanic glass Volcanic glass Solidified organic matter Solidified organic matter Appearance controlled by composition and size and arrangement of aggregate grains (texture) Appearance controlled by composition and size and arrangement of aggregate grains (texture)

Rock Types Igneous Igneous Form by solidification of molten rock (magma) Form by solidification of molten rock (magma) Sedimentary Sedimentary Form by lithification of sediment (sand, silt, clay, shells) Form by lithification of sediment (sand, silt, clay, shells) Metamorphic Metamorphic Form by transformations of preexisting rocks (in the solid state) Form by transformations of preexisting rocks (in the solid state)

Igneous Rocks Intrusive Intrusive Extrusive Extrusive

Intrusive (plutonic) Form within the Earth Form within the Earth Slow cooling Slow cooling Interlocking large crystals Interlocking large crystals Example = granite Example = granite

Extrusive (volcanic) Form on the surface of the Earth as a result of volcanic eruption Form on the surface of the Earth as a result of volcanic eruption Rapid cooling Rapid cooling Glassy and/or fine-grained texture Glassy and/or fine-grained texture Example = basalt Example = basalt

Basalt: igneous extrusive

Intrusive and extrusive igneous rocks

Sedimentary Rocks

Origin of sediment Produced by weathering and erosion or by precipitation from solution Produced by weathering and erosion or by precipitation from solution Weathering = chemical and mechanical breakdown of rocks Weathering = chemical and mechanical breakdown of rocks Erosion = processes that get the weathered material moving Erosion = processes that get the weathered material moving

Sediment types Clastic sediments are derived from the physical deposition of particles produced by weathering and erosion of preexisting rock. Clastic sediments are derived from the physical deposition of particles produced by weathering and erosion of preexisting rock. Chemical and biochemical sediments are precipitated from solution. Chemical and biochemical sediments are precipitated from solution.

Clastic Chemical/biochemical

Lithification The process that converts sediments into solid rock The process that converts sediments into solid rock Compaction Compaction Cementation Cementation

Cemented sandstone

Metamorphic Rocks

Regional and contact metamorphism

conglomerate metaconglomerate

granite gneiss

The Rock Cycle