igneous rock Flashcards
(19 cards)
What is a rock?
A rock is a naturally occurring solid mixture of one or more minerals or matter
Leucocratic means..
light colour
Mesocratic means..
intermediate colour
Melanocratic means..
dark colour
Felsic rocks are..
Rich in light coloured minerals
Mafic rocks are…
rich in dark coloured minerals
How do igneous rocks form
They forms when the rock is heated and pressure is released which causes rock to change composition
Define extrusive rocks
Rocks that form above ground when lava flows from a volcano
Define intrusive rocks
Rocks that form underground from magma
Texture of igneous rocks
Depends on size and shape of crystals when rock forms and also the cooling rate of rocks
What happens when rocks cool rapidly?
It produces fine grains and small crystals
Extrusive rocks
Example Andesite
What happens when rock cools down slowly?
It produces coarse grains with large crystals
Instrusive rocks
Example Diorite
Types of textures in igneous rocks
Aphanitic
Phaneritic
Prophyritic
Vesicular and Glassy
Aphanitic
fine grained
Phaneritic
grains can be seen by the naked eye
Porphyritic
larger grains in finer grains
Mineral composition consists of mainly
Low silicates
High silicates
What is meant by low silicates?
Low amounts of silica produce dark coloured rocks
What is meant by high silicates?
High amounts of silica produce light coloured rocks
