Igneous Rocks Flashcards
Igneous facts
over 700 different types
make up 95% of upper part of earths crust
formed by magma,
minerals have large crystals
intrusive
igneous rocks below ground
extrusive
igneous rocks on the surface
melting processes
increase in temp
decrease in pressure
change in composition
Igneous classifications
- intrusive plutonic rocks (5-10 km)
- extrusive plutonic rocks (1-3 km)
- volcanic rocks
plutonic rocks
rocks formed in the ground
Intrusive plutonic rocks
syenite granit granodiorite diorite gabbro peridotite dunite
syenite
intrusive, mostly orthoclase feldspar w/little or no quartz and little bits of mafic minerals
granite
from continental crust (from acid magma)
density: 2.7-8
high silica content
=quartz(25%)+mica+feldspars(60%) in solid solution
granodiorite
intermediate form between granit and diorite
contains more plagioclase feldspar than granite
gabbro
medium silica content
similar to granit in composition
underneath ocean
peridotite
dense course grained igneous rock, mostly olivene and pyroxene
rich in magnesium
diorite
high silica content (acidic_
common in mountainous rings of pacific ocean
Dunite
over 90% olivine
Extrusive Plutonic Rock
fast cooling, small crystals Rhyolite Dacite Andesite Basalt
Rhyolite
medium silica content
fine grained
dacite
quartz rich extrusive rock
constituent of volcanoes
Andesite
forms volcanic arcs
density>2.8
dark/dense
Basalt
most abundant rock
forms ocean crust (basic magma
low silica (basic
dark/dense (2.9(
Volcanic rocks
aka, pyroclastic rocks
debris ejected by volacnoes
fine granined
sometimes so fast cooling that it becomes glass (obsidian)
Tuff
volcanic material consolidate and lithified after deposition
constituents = crystal tuff, rock fragments (lithic tuff), or pumice/glass (vitric tuff
mostly rhyolitic
lots of quartz
high resistance to weathering
tuff fabric/foliation
foliation indicates orientation of deposition.
most common fabric in tuff is welding fabric
volcanic breccia
composed of angular mineral fragments embedded in a matrix
product of explosive eruptions
grain size
coarse (granite) >5 mm slow cool
medium 1-5 mm
fine (rhyolite) <1 mm fast cool
glassy (obsidian) invisible really fast
main features (igneous)
mode of occurence grain size of minerals total SiO_2 content other chemical composition mineral composition 2 sets of data for classification.
igneous rocks in HK
mostly acidic intruding magma (light colored, lots of quartz/feldspar)
3 types, granite, granodiorite, quartz monzonite
volcanic rocks in HK
occupy about 50% land surface area
came from middle jurassic to early cretaceous period
yim tin tsai formation
oldest volcanic rock formationin HK
crystal tuff containing hornblende
rock strength
Intrusive Extrusive Volcanic
small————————>Large
ultra-basic Basic Neutral Acid _____________________________________________________________________________________________________
Resistance to Weathering
Intrusive Extrusive Volcanic
low————————>high
ultra-basic Basic Neutral Acid ___________________________________________________________________________________________________
