Igneous Rocks Flashcards
What are the two categories an Igneous Rock can fall under?
Intrusive and Extrusive
What are extrusive rocks?
- formed above ground
- lava
- pyroclastic material (Explody volcano bits)
- fine grained
- Cools quickly
What are intrusive rocks?
- formed underground
- large crystals (phenocrysts)
What is a Mafic rock?
- made up of minerals (dark)
- iron and mg
- basalt (extrusive)
- gabbro (intrusive)
What is a Felsic rock?
- made up of aluminum silicates (light)
- lighter colours
- rhyolite (extrusive)
- granite (intrusive)
What is a dike?
When magma moves up through a rock vertically/at an angle and cross cuts. Doesn’t make it to the surface
What is a Sill?
magma intrudes and moves along the surface of a rock. (Flat)
What is a stock?
makes it all the way up to the volcano and gets extruded.
What is a pyroclastic?
explosive material from a volcano
What is country rock?
Sedimentary rock that has been intruded.
What is a vein
Contains gold, platinum, ect.
What is lava called before it makes it to the surface?
Magma
What is a Flood Basalt?
Result of a giant volcanic eruption. It is made of basalt and is a huge contributor to mass extinction
Mafic Magma
-more runny
Silica rich magma
- more explosive
- viscous
- more pyroclastic material
What are the two ways extrusives can come out of a volcano?
- lava
- pyroclastics (the size of the rock itself.)
- eg; volcanic ash vs volcanic bomb
What is porphyry
- course grains forming slowly under the earth.
- erupts quickly.
What is a Felsic rock mostly made up of?
- Orthoclase Feldspar
- Quartz
- Plagioclase feldspar
- Muscovite
What is a Mafic rock mostly made up of?
- Pyroxene
- Olivine
- Some plagioclase
Mafic Lavas
- high Fe/Mg and low silica content (dark in colour),
- they erupt at 1000-1200oC, and
- highly fluid (can travel at speeds of 100 km/hr).
- Basaltic
Intermediate Lavas
-andesitic
-they have an intermediate composition
between basalt and rhyolite.
-intrusions of intermediate magma form diorite
Rhyolitic Lavas
-low Fe/Mg and high silica content,
-they erupt at 800-1000oC,
-highly viscous (they travel 10 times slower than basalt),
because of its viscosity, it resists flow
-the vesicular variety of rhyolite is called “pumice”.
How do magmas form?
- Magmas start out felsic and become mafic by melting rocks above it.
- Subducting rock partially melts since the minerals melt at different temperatures.
What are the two main ways of changing magmas composition?
- Subduction which causes magma to move up.
2. Melting rocks around it.
Xenoliths
country rock that has melted into the magma.
What is decompressional melting?
Mantle (up) pressure (down). This causes solid rock to melt without the introduction of additional heat.
What is magmatic differentiation?
- when different minerals crystallize at different temperatures
- composition of the parent magma changes from its initial ultramafic composition
