Igneous Rocks Flashcards
What are the 3 main classes of minerals?
- Igneous
- Sedimentary
- Metamorphic
What is the Rock Cycle
a concept in geology of dynamic changes that take place on Earth to transform members of one rock class to another
Name the 2 characteristics of rocks
- Composition
- Texture
- Sometimes additional geological structures within the rock
How do igneous rocks form?
Magma cools and crystallizes
How are extrusive rocks formed?
when magma rise and extrude at earth’s surface via volcanoes
quick cooling = extrusive (volcanic) igneous rocks
How are intrusive rocks formed?
Magma trapped below Earth’s surface
cool slowly = intrusive (plutonic) igneous rocks
Describe the texture of igneous rocks.
Slow cooling below earth’s surface = large crystals
Rapid cooling at/above earth’s surface = tiny or no crystals
Describe mineral composition
Magma formed + cooled at high temp
- enriched in ferromagnesian silicate minerals
- DARK ROCKS
Magma formed + cooled at low temp
- smaller amt of ferromagnesian silicate minerals
- LIGHT COLOURED ROCKS
What is Phaneritic Texture?
Minerals are easily seen to unaided eye
- cooling is slow + at great depth
- allows crystals to grow
What is aphanitic texture?
minerals are too small to be seen with unaided eye (need microscope)
- cooling is fast at or near surface
- little time for crystals to grow
What is glassy texture?
mineral crystals are absent
- lava quenched (immediately cooled at surface)
- no time for crystals to grow
ex. obsidian
What are ferromagnesian silicates
silica w/ iron +/or magnesium
dark-coloured
What are non-ferromagnesian silicates
no iron/magnesium
light-coloured
Name the igneous compositions
felsic: light coloured
intermediate: equal light + dark minerals
mafic: dark coloured
Temperature + pressure ____ w/ depth
increase
