7 Things About Igneous Rocks You'll Kick Yourself for Not Knowing
According to their origin, rocks are divided into three groups, namely,
The igneous Rocks,
The metamorphic and
The sedimentary rocks.
|
|
Igneous Rocks formation
|
Igneous Rocks
-
Igneous rocks are formed when hot molten rock material called magma
solidifies. Magmas are developed when melting occurs either within or
beneath the Earth’s crust, that is, in the upper mantle.
-
They comprise hot solutions of several liquid phases, the most conspicuous
of which is a complex silicate phase. Thus, igneous rocks are composed
principally of silicate minerals.
-
Furthermore, of the silicate minerals, six families – the olivines
[(Mg,Fe)2SiO4],the pyroxenes [e.g. augite, (Ca, Mg, Fe, Al)2(Al,Si)2O6],
the amphiboles [e.g. hornblende,(Ca,Na,Mg,Fe,Al)7-8(Al,Si)8O22(OH)2], the
micas [e.g. muscovite, KAl2(AlSi2)10(O,F)2; andbiotite,
K(Mg,Fe)2(AlSi3)O10(OH,F)2], the feldspars (e.g. orthoclase, KAlSi3O8;
albite,NaAlSi3O8; and anorthite, CaAl2Si2O8) and the silica minerals (e.g.
quartz, SiO2) – are quan-titatively by far the most important
constituents.
-
Igneous rocks may be divided into intrusive and extrusive types, according
to their mode of occurrence.
-
In the former type, the magma crystallizes within the Earth’s crust,
whereas in the latter, it solidifies at the surface, having erupted as
lavas and/or pyroclasts from a volcano.
-
The intrusions have been exposed at the surface by erosion.
-
They have been further subdivided onthe basis of their size, that is, into
major (plutonic) and minor (hypabyssal) categories.
