Igneous Rocks Flashcards
1
Q
Aphanitic
A
- fine crystals (only visible with microscope)
- forms from rapid cooling close/at the surface
- may have vesicular texture
2
Q
Phaneritic
A
- course crystals
- Slow cooling magma formed deep within the Earth’s crust.
- can be identified with naked eye
- crystals roughly equal in size
3
Q
Porphyritic/porphyry
A
- large crystals surrounded by smaller crystals
- Large crystals called phenocrysts form in magma at depth.
- Magma erupts and Rapid cooling within produces fine grained crystal groundmass
4
Q
Glassy
A
- no crystals because of instantaneous cooling
5
Q
Pyroclastic
A
- Not crystals but individual rock fragments
- Rock fragments from violent volcanic eruptions combine to form an igneous rock.
6
Q
Pegmatitic
A
- very course crystals larger than 1cm diameter
-Formed in the fluid-rich, late stages of magma crystallisation. - can contain rare and valuable minerals
7
Q
Ultra-mafic
A
- less than %45 silica
- olivine and pyroxene minerals
- calcium rich plagioclase feldspar
- aphanitic eg komatite
- phaneritic eg peridotite
8
Q
Mafic
A
- 45-52% silica
- Pyroxene, calcium-rich plagioclase feldspar minerals
- also some Amphibole, Olivine
- aphanitic eg basalt
- Phaneritic eg gabbro
9
Q
Intermediate
A
- 52-70% silica
- Amphibole, sodium and calcium-rich plagioclase feldspar minerals
- some Pyroxene and biotite
- apharatic andesite
- phaneratic diorite
10
Q
Felsic
A
- 70+% silica
- Quartz, potassium feldspar, sodium-rich plagioclase feldspar minerals
- some Amphibole
Muscovite, Biotite - apharatic eg Rhyolite
- phaneratic eg Granite
