Rocks that crystallized directly from a melt Igneous rocks Form as magma cools and crystallizes Rocks formed inside Earth are called plutonic or intrusive rocks Rocks formed on the surface ID: 495624
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Slide1
Igneous Rocks
Rocks that crystallized directly from a meltSlide2
Igneous rocks Form as magma cools and crystallizes
Rocks formed inside Earth are called
plutonic
or intrusive rocks
Rocks formed on the surface
Formed from
lava
(a material similar to magma, but without gas
Called
volcanic
or extrusive rocksSlide3
Igneous rocks
Crystallization of magma Fractionation: mineral separation in a magma chamber based on crystallization temperatures
Ions are arranged into orderly patterns
Crystal size is determined by the rate of cooling
Slow rate forms large crystals
Fast rate forms microscopic crystals
Very fast rate forms glass Slide4
Igneous rocks
Classification is based on the rock's texture and mineral constituents
Texture
Size and arrangement of crystals
Types
Fine-grained
– fast rate of cooling
Coarse-grained
– slow rate of cooling
Porphyritic
(two crystal sizes) – two rates of cooling
Glassy
– very fast rate of cooling
Slide5
Classification of igneous rocksSlide6Slide7Slide8Slide9
Mafic magma can become felsic magma as it cools! Bowens Reaction Series tells us that:
As a magma chamber cools, the mafic minerals crystallize first, then felsic ones
As minerals crystallize out, the gas is left behind in the felsic melt…Slide10
The main factor contributing to crystal size is rate of cooling!
Textures based on crystal size:
Aphanitic
: almost no visible crystals
Porphyritic
: large crystals in a matrix of smaller crystals
Phaneritic
: interlocking large crystals
Vesicular
: full of holes (vesicles)
Glassy
: resembles glass
Pyroclastic
: made up of fragments (often ash and pumice)
Slide11
Intrusive (Plutonic)Mafic- roots of plutons
GabbroIntermediate- near the base of plutons
Diorite
Felsic- most plutons (very common!)
GraniteSlide12
Extrusive (volcanic)
Mafic
- shield volcanoes, cinder cones, ocean basalts
Basalt
Scoria
Intermediate- composite cones
Andacite
Dacite
(more felsic)
Felsic- domes and
pyroclastic
deposits
Rhyolite
Tuff
Obsidian and pumiceSlide13
Fine-grained igneous textureSlide14
Course-grained igneous textureSlide15
Porphyritic igneous textureSlide16
Obsidian exhibits a glassy texture