Litho: Classification Of Rocks Flashcards
How are igneous rocks formed?
Via the solidification of molten rock material. They are made of interlocking crystals of minerals. As molten magma cools, crystallisation of these minerals solidifies and forms the rock.
What are the 3 different types of rocks?
Igneous, sedimentary and metamorphic
What are the types of igneous rocks?
Intrusive (plutonic) and extrusive (volcanic)
What are the places of formation of intrusive and extrusive igneous rocks?
Intrusive - under the surface (as material from the mantle forces its way to the crust, solidifying as it moves)
Extrusive - above the surface
What are the differences in texture of igneous rocks?
Intrusive - Phaneritic (coarse-grained) as lava cools much slower underground, hence they have more time to grow before solidification.
Extrusive - Aphanitic (fine grained) as lava cools more quickly, leaving less time for crystals to grow.
How are sedimentary rocks formed?
Diagenesis or precipitation
How are sedimentary rocks classified?
Mechanical, chemical, organic
How are sedimentary rocks of mechanical origin formed?
derived from elsewhere and transported as solid particles to the site of deposition through weathering or erosion.
Diagenesis - compaction and cementation due to unstable environment that is hotter (>200degrees) and has higher pressure. Diagenesis occurs as materials move deeper and get buried as more sediment is deposited above it. Diagenesis causes the clasts to be bound together and turned into rock
How are sedimentary rocks of chemical origin formed?
Very close to the ultimate site of deposition and commonly mixed with detrital sediments such as mud
How are sedimentary rocks of organic origin formed?
By accumulation of organic matter in the form of plant and animal remains.
Diagenesis - remains of sea creatures subjected to diagenetic processes. Eg. Limestone
How are metamorphic rocks formed?
They form under high pressure and heat where they undergo metamorphism. Minerals in preexisting Rock will change and alter the whole mineral composition of the rock when it’s in an unstable environment.
What are the types of metamorphism?
Contact metamorphism & Regional metamorphism
How does contact metamorphism occur?
Occurs when a rock comes into contact with a source of extreme heat such as igneous intrusion. Eg. Batholiths.
Temperature increases and rocks within a distance may be affected. Degree of alteration of rocks decrease with increasing distance from intrusion.
How does regional metamorphism occur?
Occurs when large areas are subjected to tectonic forces, such as mountain ranges at convergent plate margins. Increase in both temp and pressures leads to metamorphic grading. This gives them a layered appearance called a foliates texture. Eg. Schist and Gneiss
