Igneous Rocks Flashcards
what colour are primary igneous rocks?
dark/black
ie gabbro
what is a primary igneous rock?
basalt that has been erupted from a volcano
how can we classify rocks?
whole rock chemical composition
mineralogical composition of rock
modal composition of rock
what do we call a rock of pure olivine?
dunite
what minerals do you expect within a basalt?
plagioclase
clinopyroxene
mica
feldspar
olivine
what is removed from olivine when crystalising?
Mg
Fe
what is removed from pyroxene when crystalising?
Mg
Fe
Ca
what is removed from plagioclase when crystalising?
Ca
Na
Al
what is removed from amphibole and micas when crystalising?
K
Al
What percentage of olivine is SiO2?
40%
what happens when there is more silica content than cations?
doesnt have anything to react with therefore reacts with itself SiO2 to form quartz
what are the sources of igneous rocks?
crust: igneous, sediment, metamorphic
mantle: fertile or depleted
erupts at surface
what end member of plagioclase has the highest melting point?
Anorthite (instead of albite)
Calcium rich
stronger bonds need more energy to break
what does 5GPa equate to?
when diamond forms
150km depth
why do we refer to mantle as fertile?
contains minerals that can melt
ie has pyroxenes –> basalt
why do we refer to mantle as depleted?
contains only olivine, needs 1800 degrees C to melt therefore typically doesnt
what happens everytime you melt the mantle?
purify it ie makes it more olivine in composition
spew out what earth doesnt what ie Al,
what do we call slow and fast growth?
slow growth = monocrystalline (large crystals)
fast growth = polycrystalline
what is quenched texture?
needle like shapes formed by fast cooling
crystals floating in a sea of liquid(now solid) rock
typical of basalt
what is the evolution of basalt?
basalt -> andesite -> rhyolite
at what speeds do basalts and rhyolites flow?
basalts very slow - iceland
rhyolites very fast get out - mt pinnatubo
