Download igneous rocks

TYPES OF ROCK
 If an igneous rock is intrusive (plutonic) that means it formed and
cooled under the Earth’s surface (crust) and since the temperatures
are greater at this level the rocks would take longer to cool.
 If an igneous rock is extrusive (volcanic) that means it formed on or
close to the Earth’s surface where temperatures are cooler than deep
within the earth. This would give the igneous rock samples small or
possibly no crystal structure at all.
ROCK EXAMPLES
 intrusive igneous rocks: diorite, gabbro, granite and pegmatite .
 extrusive igneous rocks: andesite, basalt, obsidian, pumice, rhyolite
and scoria.
Obsidian
Scoria
Pumice
GEOLOGICAL SIGNIFICANCE
 their minerals and global chemistry give information about the
composition of the mantle, from which some igneous rocks are
extracted.
 their absolute ages can be obtained from various forms of radiometric
dating and thus can be compared to adjacent geological strata.
 their features are usually characteristic of a specific tectonic
environment, allowing tectonic reconstitutions.
 Igneous rocks help us determine if there is or was thermal activity
going on inside the rocks layers.
CLASSIFICATION
 Igneous rocks are classified according to mode of occurrence, texture,
mineralogy, chemical composition, and the geometry of the igneous
body.
 Two important variables used for the classification of igneous rocks
are particle size, which largely depends on the cooling history, and the
mineral composition of the rock.
 In a simplified classification, igneous rock types are separated on the
basis of the type of feldspar present, the presence or absence of
quartz.
IGNEOUS DIFFERENTIATION
Igneous differentiation is a general term for processes that change the
compositions of magmas and the igneous rocks that they produce. The
three most important processes that cause igneous differentiation are
crystal fractionation, crustal contamination and magma mixing. In some
magmas liquid immiscibility can also be important.
WHERE ARE IGNEOUS ROCKS FOUND?
The most common igneous rock Basalt (mafic) makes up most of the
oceanic plates and is founds at divergent plate boundaries. In fact most
igneous rock activity occurs at divergent plate boundaries. However,
intermediate to felsic igneous rocks are most commonly found along
continental margins.