igneous rock Flashcards
petrology
study of rocks
lava vs magma
lava is magma that has erupted
igneous rocks form from….
cooling of magma
3 ways of magma formation
- decompression melting (pressure drop)
- flux melting (add volatiles H2O CO2 SO2)
- heat transfer from rising magma
_______ magma is the most abundant magma, it is of ________ composition and generated in the ______
mafic magma is the most abundant magma, it is of basaltic composition and generated in the mantle
_________ and ______ magmas are of ________ to rhyolitic composition, and are generated in the _____
intermediate and silicic magmas are of andesitic to rhyolitic composition, and are generated in the crust
how does addition of volatiles help melt mantle rock? what type of magma is formed
- break molecular bonds
- decreases melt temp
- basaltic magma (mafic) formed
magma is _______ (silicic) if melted crust alone rises in Heat transfer
magma is rhyolitic (silicic) if melted crust alone rises in Heat transfer
formation of andesitic (intermediate) magma in heat transfer
basaltic magma and melted crust mix
BOWEN’s Reaction series
dictates what minerals crystalise at what temperatures
according to BOWEN’s reaction series, what crystallises at high T and Low T
high T- Mafic minerals
low T- Felsic minerals
three igneous rock textures
- Aphanitic - fine
- Phaneritic - coarse
- Porphyritic - large phenocrysts in fine matrix
eg of aphanitic
basalt
eg of phaneritic
gabbro
eg of porphyritic
andesite
magma thats cooled over centuries would form
phaneritic texture
main way to classify igneous rock, based on chemical composition
silica content (SiO2)
most silica = ,
least silica = , and ,
most silica = silicic,
least silica = mafic, ultramafic and ,
3 environments igneous rock forms in
- Plutonic environment - High P, slow cooling
- subvolcanic/ hypabyssal - transitional
- volcanic
- low P, fast cooling
most common plutonic rock in the continental crust
granite
gabbro (mafic) forms significant part of what?
oceanic crust
how are plutonic rocks found on the surface of the earth?
by uplift and erosion
peridotite is what type of mineral?
ultramafic
example of intermediate, phaneritic rock
Diorite
dyke
cross-cutting, flat sheet cuts across rock layers
sill
parallel to local structures
effusive volcanic activity
- forms crystalline rock
- magma extruded at the ground surface
- little gas involved
explosive volcanic activity
forms clastic rock
2 variances of rhyolite
Pumice and obsidian
basalt forms from ___ viscosity lava. Andesite forms from ___ viscosity lava. Dacite forms from ____ viscosity lava.
low, medium, medium-high
IGNIMBRITE
pumice-dominated (glassy) pyroclastic flow deposits
2 major groups of igneous rocks
- volcanic - extruded onto the earths surface
2. plutonic - cooled from magma inside the crust
having same chemical composition what are the plutonic equivalents of:
Basalt =
Andesite & Dacite =
Rhyolite =
Basalt = Gabbro
Andesite & Dacite = Diorite
Rhyolite = Granite
Basalt colour and varieties
dark grey. Vesicular variety and Scoria variety
some uses of Basalt include…
aggregate, fill in construction, armour rock, scoria for drainage
colour of andesite vs basalt
lighter grey
Andesite uses
aggregate fill in roading and construction (not good in concrete due to high silica)
Rhyolite is light-coloured, name 3 varieties:
- Obsidian (glassy)
- pumice (vesicular)
- Ignimbrite (lithification of ash and pyroclastic flow)
Gabbro colour and uses
very dark black. Used as aggregate and as a building stone in foyers etc. (‘black granite’)
what will happen if an aggregate with high silica content or glass is used in cement?
reacts with cement to produce swelling materials which will result in cracking
what mineral would be good in an aggregate for cement?
ferromagnesium
would granite bind well with bitumen? why/why not?
NO, it has large mineral grains
