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Intrusive and extrusive igneous environments
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Batholith
What it is: Giant blobs of cooled magma deep underground in earth’s crust. Intrusive/plutonic
Formed from: Many intrusions over time.
Rock type: Usually granite or diorite.
Dike
What it is: A vertical sheet of magma that cuts across existing rock layers. Intrusive/plutonic
Think: Like magma crashing the party and slicing through everyone’s vibes.
Orientation: Discordant (cuts across bedding).
Rock type: Can be anything from basalt to rhyolite.
Sill
What it is: A horizontal intrusion between rock layers. Intrusive/plutonic
Think: Magma being sneaky and sliding between the bedsheets.
Orientation: Concordant (parallel to bedding).
Laccolith
What it is: Magma spreads out horizontally, pushing the overlying layers of rock upwards and creating a dome. Intrusive/plutonic
Rock type: Often felsic (e.g., rhyolite or granite).
Fun fact: Forms mini-mountains.
Lava flow
What it is: Magma that makes it to the surface and flows like hot syrup. Extrusive/volcanic
Texture: Fine-grained (basalt, andesite).
Types:
Pahoehoe (ropy, smooth)
Aa(chunky, rough)
Pyroclastic flow
What it is: Superheated gas, ash, and rock fragments flowing downhill FAST. Extrusive/volcanic
Rock formed: Tuff or ignimbrite (consolidated volcanic ash).
Volcanic neck
What it is: The solidified magma in the throat of a volcano after the rest erodes away. Intrusive/plutonic
Famous one: Shiprock, New Mexico.
How it forms: Intrusive, but later exposed