Download Types of Rocks

Types of Rocks
1) Igneous Rocks - all crystallize from a hot melt: magma - below sfc, lava - above sfc
- ~80% of the Earth’s crust
Types of Igneous Rocks (w.r.t. cooling)
a) Intrusive - Plutonic - from magma, coarse-grained (ex: granite)
b) Extrusive - Volcanic - from lava, fine-grained (ex: basalt)
Intrusive Bodies
a) Shallow (< 2 km)
Volcanic Neck - solidified magma of conduits that once connected a volcanic vent
to the Earth’s surface with a deep magma reservoir
Small Plutons (body of plutonic rock of any size or shape, intrusive rock - i.e. have
intruded into the host rock)
i) Dikes - discordant - cut across layers
ii) Sills - concordant - parallel to layers
Laccolith - concordant - more or less circular in shape, up to 3 km across
b) Deep
Batholith - continuous mass of granitic rock covering an area > ~100 km2, formed
by rising large blobs of magma which are less dense than surrounding rock
Stock - similar to a batholith but covers an area < 100 km2
2) Sedimentary Rocks - form from sediment deposited on the Earth’s surface, either from
weathering & erosion of pre-existing rocks or chemical precipitation from solution,
including secretions from water organisms. ~ 5% of the Earth’s crust.
Lithification - transformation of unconsolidated sediment into solid rock
Types of Sedimentary Rocks
a) Clastic - from mechanical weathering - grains are broken down by a physical process &
are deposited, consist of debris from erosion of older rocks or soil.
Examples:
i) Coarse-grained: conglomerate - formed by cementation of rounded gravel
breccia - formed by cementation of angular fragments
ii) Medium-grained: sandstone - formed by cementation of sand
iii) Fine-grained: shale - formed by cementation of silt & clay particles
b) Chemical - from precipitation from an aqueous environment - either precipitated
directly by inorganic processes or by the actions of organisms,
- consist of material formed within the sedimentary environment;
- limestone is the most abundant
3) Metamorphic Rocks - from igneous, sedimentary or other metamorphic rocks that
recrystallize under high T & P destroying old mineral grains & rock textures while
creating new mineral assemblages & distinctive metamorphic textures & structures.
Agents of Metamorphism
a) composition of parent rock
b) temperature - principal factor, can cause recrystallization & a loss of volatile compounds
(CO2, water vapor)
c) pressure - can cause recrystallization
d) fluids
e) time
Classifications of Metamorphic Rocks (based on texture)
a) Foliated - characterized by the parallel orientation of their layered minerals & varying degree
of banding (color layering)
ex: slate - from shale, schist - from shale, gneiss - from granite
b) Non-foliated - no layers
ex: marble - from limestone, quartzite - from quartz