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Minerals and Rocks. Lecture Outline. What are minerals? Common rock-forming minerals Physical properties of minerals Basic rock types The rock cycle. Minerals . A mineral is a naturally occurring, solid crystalline substance, generally inorganic, with a specific chemical composition. - PowerPoint PPT Presentation
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Minerals and Rocks
Lecture Outline
What are minerals?
Common rock-forming minerals
Physical properties of minerals
Basic rock types
The rock cycle
Minerals
Natural Solid Atoms arranged in orderly repeating 3D
array: crystalline Not part of the tissue of an organism Composition fixed or varies within defined
limits
Minerals are the “building blocks” of rock
A mineral is a naturally occurring, solidcrystalline 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
chlorideHalite
Chemical Bonds: Ionic
Electrical attraction between ions of opposite charge Bond strength increases with the electrical charges of the
ions Bond strength decreases as the distance between the
ions increases Most minerals are this kind of compound
Na+ Cl-
Ionic Bonding example:halite
AnionCation
Covalent Bonds: Electron sharing Generally stronger than ionic bonds (e.g., diamond)
Crystallization of Minerals
Need starting material with atoms that can come together in the proper proportions Growth from a liquid or a gas
Time and space for crystallization
Appropriate temperature and pressure
Examples Magma that has cooled below its melting point Supersaturated solution --> precipitation
Crystallization of Minerals
Crystals begin as an initial “seed” - a microscopic crystal
Atoms keep being added in a 3D array, repeating the basic arrangement
Crystal faces are based on the array structure
Cations and Anions
Anions are typically large
Cations are relatively small
Crystal structure is determined largely by the arrangement of the anions
Common cations and anions
Radii given in angstroms; 10-8 cm
Ions can be compound So far, we’ve talked about individual atomic
ions Many common minerals are silicates
SiO44-
Complex ions act as a single ion in forming crystal structure
Cation Substitution
Crystal structure determined by those large anions
Various cations can substitute for each other in many minerals Same crystal structure Different chemical composition
PolymorphsMinerals with the same composition,
but different crystal structure.
Common Rock-Forming MineralsMinerals fall into a small number of related “families” based mainly on the anion in them
Silicates Most abundant minerals in the Earth's crust Silicate ion (tetrahedron), SiO4
4-
Quartz (SiO2), K-feldspar (KAlSi3O8), olivine ((Mg, Fe)2SiO4), kaolinite (Al2Si2O5(OH)4)
Quartz (SiO2)
Silicate structure Most of the most common rocks in the crust
are silicates Silicate tetrahedra can combine in several
ways to form many common minerals Typical cations:
K+, Ca+, Na+, Mg2+, Al3+, Fe2+
Different numbers of oxygen ions are shared among tetrahedra
Carbonates
Cations with carbonate ion (CO32-)
Calcite (CaCO3), dolomite (CaMg(CO3)2), siderite (FeCO3), smithsonite (ZnCO3)
Make up many common rocks including limestone and marble
Very important for CCS!
Calcite (CaCO3)
CaCO3 + 2H+ = Ca2+ + CO2 + H2O
Smithsonite (ZnCO3)
Oxides
Compounds of metallic cations and oxygen
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
Hematite (Fe2O3)
Sulfides
Metallic cations with sulfide (S2-) ion Important for ores of copper, zinc, nickel, lead, iron Pyrite (FeS2), galena (PbS)
Galena (PbS)
Sulfates
Minerals with sulfate ion (SO42-)
Gypsum (CaSO4.H2O), anhydrite (CaSO4)
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)
Crystal structure (X-ray diffraction)
Physical properties
Physical properties
Hardness
Physical properties Hardness
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
Cleavage
Fracture: tendency to break along other surfaces (not cleavage planes)
Conchoidal fractures
Physical properties Hardness Cleavage Fracture Luster (metallic, vitreous, resinous, earthy, etc.) Color (often a poor indicator; streak color is better) Specific gravity 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 Volcanic glass Solidified organic matter Appearance controlled by composition and size and
arrangement of aggregate grains (texture)
Rock Types
Igneous Form by solidification of molten rock (magma)
Sedimentary Form by lithification of sediment (sand, silt, clay,
shells) Metamorphic
Form by transformations of preexisting rocks (in the solid state)
Igneous Rocks
Intrusive Extrusive
Intrusive (plutonic)
Form within the Earth Slow cooling Interlocking large crystals Example = granite
Extrusive (volcanic)
Form on the surface of the Earth as a result of volcanic eruption
Rapid cooling Glassy and/or fine-grained texture 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
Weathering = chemical and mechanical breakdown of rocks
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.
Chemical and biochemical sediments are precipitated from solution.
Clastic
Chemical/biochemical
Lithification
The process that converts sediments into solid rock Compaction Cementation
Cemented sandstone
Metamorphic Rocks
Regional and contact metamorphism
conglomerate
metaconglomerate
granite
gneiss
The Rock Cycle
The Rock Cycle