Rocks Flashcards
3 groups of rocks
- igneous (hot rocks/fire)
- sedimentary
- metamorphic
Rocks
-Made up of minerals
-Makes up the geosphere
Most rocks are made of several minerals but some are monomineralic (one mineral)
Igneous
Rocks formed by crystallization of magma/lava during cooling
Sedimentary
Formed at or near earth’s surface from sediment that may include mineral or rock fragments, organic fragments (sandstone), by precipitation from water (limestone)
Metamorphic
Formed from igneous, sedimentary or previously metamorphosed rocks by heating and/or increase in pressure during collision of tectonic plates or magma intrusion
Major environment issues associated with igneous activity
- volcanic hazards
- sources of many ore deposits
- driving energy and nutrients for some important ecologic systems
- driving energy for geothermal systems
- building materials
Igneous rocks
(intrusive vs extrusive)
(plutonic vs volcanic)
-lava flow (volcanic/extrusive)
-magma chamber (plutonic/intrusive)
Plutonic vs volcanic:
-plutonic (slowly cooled)
-volcanic (rapidly cooled)
Igneous rock
Ferromagnesian (dark color)
- olivine
- pyroxene
- amphibole
- biotite
Igneous rock
Felsic (light color)
- plagioclase feldspar
- orthoclase feldspar
- Quartz
- muscovite
Things that control igneous rock composition
- composition of the source
- magnetic differentiation
Provenance of igneous rock composition
- mantle is made of peridotite
- mantle source -> basalt, andesite, dacite (and their plutonic equivalents: gabbro, diorite, granddiorite)
- continental crust source -> rhyolite (and it’s plutonic equivalent: granite)
Magmatic differentiation
-process by which a homogenous magma segregates into different rock types
Magmatic differentiation: sequential crystallization of minerals permits their separation
High density minerals will sink inside a magma chamber, low density minerals will float inside a magma chamber
Fractional crystallization
The separation of minerals, it is the most common type if magmatic differentiation
Making of sedimentary rocks
1) weathering
- mechanical (erosion, breaking rocks apart)
- chemical (chemical reactions)
2) sedimentation (transport and deposition)
3) Lithification
Weathering
Is the response of rocks to new conditions at or near Earth’s surface
-for example, minerals in lava that crystallized at 1000 degrees Celsius are not very stable at surface conditions
Agents of mechanical weathering (erosion)
- running water
- wind
- glaciers and ice
- ocean currents and waves
- gravity
Chemical weathering
Dissolution or transformation of original minerals to secondary minerals by interaction with various solutions
- dissolution by water
- dissolution by acid
- oxidation
- hydrolysis (diagenesis)
Properties of clay
Good properties: -filtering of toxic metals -material for pottery and construction Bad properties: -swelling of soils -soil failures (slumps, landslide)
Factors that control the extent of chemical weathering
1) composition of minerals
2) temperature
3) presence of water (humidity)
Weathering-composition of minerals
- ferromagnesian silicates weather the fastest
- K - Al silicate are more resistant to weathering
- Halides and Sulfates dissolve easily in solutions
- carbonates dissolve easily in acidic solutions
Weathering-temperature
High temp increases rate of weathering
Role of climate
Climate combined the previously noted factors
- in warm, humid climates, chemical weathering predominates
- in arid, cold climates, mechanical weather predominates
Transporting sediment
- water (fluvial transport)
- glaciers
- wind (Aeolian transport)
- gravity (Mass wasting)
Types of sedimentary rocks
-detrital
-chemical
-biochemical
A sedimentary rock may contain all 3 components
Detrital (clastic)
Pieces of pre-existing rocks and minerals litho fief together as solutions pass through and precipitate quarts or carbonate minerals
Chemical
Minerals are precipitated from seawater or lakes
Biochemical
Components that have biological origin
Common detrital sedimentary rocks
1) conglomerate: dominated by rounded granules or larger rock or mineral fragments
2) sandstone: dominated by sand-size grains
3) shale: silt or mud-sized grains
Chemical sedimentary rocks
1) limestone- mostly calcite
2) dolostone- 50% dolomite, forms by additions of Mg to calcite
3) evaporites- consist if precipitated halides, Sulfates, borates ect.
4) chert- finely crystalline silica deposited on ocean floor
sedimentary rocks with biochemical components
- Coal: converted organic matter, usually from swamps
- black shale: shale with carbonized algae
- fossil-bearing limestone
Metamorphic rocks
Metamorphism: is the response of rocks by solid state reactions and deformation to changes in temperature, pressure and chemical environment
Agents of metamorphism
- heat (200-900•c): causes mineral reactions and coarsening, ex: muscovite -> orthoclase + corundum + water
- pressure: causes mineral reactions and deformation of rocks
- hydrothermal solutions: carry dissolved elements that cause formation of new minerals (metasomatism)
Causes of metamorphism
- plate tectonics and mountain building
- intrusion of Magnus into the upper crust
Some societal issues of metamorphic rocks
- metamorphism results in the formation of some mineral ores (graphite, talc, ect.)
- many gens are metamorphic mineral (ruby, garnet, jade, ect.)
- slate and marble are important building stones
- metamorphic foliation influences groundwater flow and slope stability
Metamorphic foliation
Foliation is alignment of Micas (and other minerals) because of compression. It is common is schist, which contain high proportions of Micas
