Practical Skills - Igneous Rock Flashcards
Cooling rate of a coarse crystal?
Coarse Crystals
- long time to cool
- slow rate of cooling
What conditions will a pluton occur?
In coarse grained rocks such as granite, gabbro or peridotite
What conditions will a dyke/sill form?
In Medium grained rocks such as dolerite
What conditions would a lava flow occur?
In fine grained rock such as basalt
What are the key minerals?
Hornblende which is 120 degree cleavage intersection angle
Pyroxene which is 90 degree cleavage intersection angle
Cooling rate of fine crystal?
- quick rate of cooling
- shorter amount of time to cool
What is fractional crystallisation?
removal and segregation from the melt of mineral precipitates
leads to the change in composition of a magma
what does crystallising minerals do to them in the magma chamber?
causes them to settle at the bottom of the magma chamber
removal from melt means a change in composition
what is cumulation?
the layer at the bottom of the magma chamber/body
formed by gravity settling
what is gravity settling?
when the denser minerals sink to the bottom of the chamber via gravity
what is assimilation?
addition of country rock to a magma causes it to change composition
rocks get incorporated via stoping
blocks that don’t get fully melted are called xenoliths
what is stoping?
magma forces its way through cracks and then rips off bits of the country rock to incorporate into the melt
what is magma mixing?
when two different compositions are fluid enough to mix together
forms enclaves
normally wavy boundries
what is an enclave?
a blob of magma, with a different composition to the main host
left after incomplete mixing
