Download Minerals and Rocks Outline •Matter, Atoms, etc. •Minerals •Igneous

Minerals and Rocks
Outline
•Matter, Atoms, etc.
•Minerals
•Igneous Rocks
•Sedimentary Rocks
•Metamorphic Rocks
•The Rock Cycle
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Atoms of Chemical Elements
Basic building blocks of minerals
Composed of protons, neutrons, electrons
Protons+ Neutrons= Atomic Mass
Protons=Atomic number
Electrons=most important role in chemical bonding
Chemical Bonding—4 Types
1. Ionic- one atom loses/gains electron from its outer shell to give to/take from
another atom
2. Covalent- electrons are shared
3. Metallic- atoms share clouds of electrons
4. Van der Waals (molecular bonds)- weak secondary attraction bonds
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Rocks vs. Minerals
Rocks
– basic building blocks of Earth
– indicators of how Earth developed over geological time
– mixture of one or more minerals
Mineral
– naturally occurring
– inorganic crystalline solid
– made of chemically bonded elements
– with definite chemical composition
Crystals
Solid composed of atoms and molecules
Have ordered internal structure
Minerals occur in crystals, may not have well-defined external form
Mineraloids are non-crystalline solids (volcanic glass, opal, amber)
Mineral Groups
•Most rocks of earth’s crust =about 20 minerals
•Minerals divided into six groups based on their chemical properties
•Silicates and Carbonates groups= contribute most to rock record
Silicates
•Have silica tetrahedron (SiO4) as basic “building block” or chemical property
•Dominant group in igneous, sedimentary, and metamorphic rx
Carbonates
•Have Ca, Mg, Fe, Cu, or other ions attached to carbonate ion (CO3-)
•Important in sedimentary rx
•Can form metamorphic rock, marble
•Easily identified by their reaction to dilute hydrochloric acid (HCl)
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Halides
Have positive ions (e.g. Na, K) attached to negative ions (e.g. Cl, Br)
Commonly referred to as “salts”
Most occur in chemical (evaporite) sedimentary rx
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Oxides
Have metallic ions combined w/oxygen
Can occur in igneous, sedimentary, metamorphic rx
Iron oxide=common cement in sedimentary rocks
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Sulfates
Have calcium or other ions attached to sulfate ion (SO4-2)
Most sulfate minerals, (e.g. gypsum, anhydrite) occur in evaporite sedimentary
rocks
Sulfides
Have metallic ions combined with sulfur
Occur in igneous, sedimentary, metamorphic rx,
Most commonly associated w/metal ores
Biomineralization
•Secretion of minerals (bones, teeth, shells, external coverings, etc.) by critters
•Most common element = calcium, usually in carbonate or phosphate
• Hard parts later become fossilized remains in rock
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The Rock Cycle
Igneous Rocks
Molten rock, including any suspended crystals (mineral grains) and dissolved
gases
– magma = below land surface
– lava = above land surface
Igneous rocks are formed from cooling and crystallization of magma or lava
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Sedimentary Rocks
Usually layered, formed from seds, minerals precipitated under water
Sediments=
– unconsolidated particles
• rock transported by agents of erosion
• formed through biomineralization
Metamorphic Rocks
Original mineralogy, texture = transformed w/ heat, pressure, chemical
environment (including hydrothermal fluids), or shearing stress
Commonly associated w/tectonic activity
Classification of Rocks
•Rocks can be classified in two ways:
•Descriptive classification system - according to texture or fabric, composition
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2) Genetic classification system –according to origin
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Classifying Igneous Rocks
Chemical composition:
– Light-colored (felsic)
– Dark-colored (mafic)
– In between Dark & Light (intermediate)
Igneous Rock Textures (used for ID, based on Origin)
Extrusive Rocks (outside earth):
•Glassy=Like a Jolly Rancher
–obsidian
•Vesicular=lots of bubbles=Rice Crispy Treat
–Frothy= vesicular on steroids
–pumice, scoria, vesicular basalt
•Aphanitic (fine-grained)=sugar cookie
–rhyolite, andesite, basalt, komatiite
•Fragmental (breccia)=chunks of stuff
–volcanic breccia, tuff
Intrusive Rocks (inside earth):
•Phaneritic (medium-coarse grained)=oatmeal cookie
–Granite, diorite, gabbro, peridotite
•Pegmatitic (very coarse-grained, >2 cm)=Like a brownie
–granite pegmatite
•Porphyritic (2 distinct grain sizes)=Like a chocolate chip cookie
–diorite porphyry, andesite porphyry, etc.
Igneous Rock ID
Sedimentary Rocks
• Diagenesis=all processes that change sediments to rock
• Sed. particles from three main sources:
1. Fragments (clasts) produced by weathering of rocks/minerals
2. Skeletal debris produced by organisms
3. Crystals precipitated from water, commonly associated with
biological activity
Classifying Sedimentary Rocks
• Classified based on composition
• Principal categories:
– Siliciclastic rocks
– Carbonate rocks
– Other sedimentary rocks
Forming Sedimentary Rocks
• Deposition of sediments
– layer by layer (sedimentary bedding or lamination)
– Various scales upward from millimeter-scale layering
– Key feature of sed. Strata, one of primary characteristics of sed. rx
• Grain shape and sorting =important characteristics for identification
• Lithification =compaction of seds & cementation
• Cementation = precipitation of minerals from water
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Metamorphic Rocks
•alteration of other rocks at high temps & press.
•Causes chemical and textural changes in any and all other rocks
•Described in terms of “grades” that reflect temp and press that altered rocks
Classifying Metamorphic Rocks
Foliation
– Common distinguishing characteristic of metamorphic rocks
– alignment of crystals that have grown perpendicular to direction of stress
applied to rock during metamorphism
Not all metamorphic rocks are foliated, e.g. single-mineral composition rocks like
marble (non-foliated)
Metamorphism
•Low-grade metamorphism
–Between 100˚C-200˚C
–Tend to be fine-grained
•High-grade metamorphism
–Above 500˚C
–Tend to be coarse-grained
•Foliation in coarsely crystalline rocks = wavy, distorted
•Temperature, pressure, chemical fluids, and type of rock affect grade
•Regional metamorphism
–Mountain building, subduction zones
–Greatest volume of metamorphic rock
•Contact metamorphism
–Cool rock+hot rock meet=hot rocks “cooking” cool rocks
–Produces well-defined zones of metamorphic grades across intrusion
•Burial metamorphism
–Increases pressure and temperature
–Coal is formed from peat
•Hydrothermal metamorphism
–Hot water, chemically active fluids added to mix
–Often responsible for economic metals
•Impacts
•Occurs when high speed projectiles (meteorites) strike Earth’s surface
•Products = impactites
•Faults
•Occurs at depth, high temps.
•Pre-existing minerals deform by ductile flow
•Migmatites
•Highest grade of metamorphism that is transitional to igneous rocks
•Contain light bands of igneous components along w/areas of unmelted
metamorphic rock