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.
