Geology Chapter 4
gabbro
mafic, phaneritic
lava
magma on or above earths surface
Four compositional groups of igneous rocks in order from highest to lowest silica content
1. felsic 2. intermediate 3. mafic 4. ultramafic
Pegmatitic
Crystals larger than 1 cm
rhyolite
Felsic, Aphanitic
blast
mafic, aphanitic
Which of the following describes an aphanitic texture?
Rock is crystalline, grains to small to see with naked eye
plutonic
Synonym for intrusive
Peridotite
Ultramafic, Phaneritic
Processes magma undergoes to become igneous rock
a. cooling b. solidification c. crystallization
which paneritic igneous rock is compose mostly go quartz and potassium feldspar?
a. granite b. quarts and potassium feldspar
Factors affecting crystal size
a. length go time allowed for cooling (longer time=bigger crystals) b. amount of silica present (more=bigger crystals) c. amount of dissolved gases
which igneous rock have glassy textures?
a. obsidian b. pumice
What texture would typically result from a single, long period of cooling and crystallization?
a. pegmatitic b. phaneritic
Phaneritic
all crystals visible to the make eye (intrusive)
magma
all molten rock
Obsidian
compact volcanic glass, sometimes felsic
Pyroclastic
composed of broken pieces of volcanic rock and debris
Porphyritic
crystals are two different sizes texture: phaneritic or aphanitic
Aphanitic
crystals to small to see with naked eye or no crystals (extrusive)
granite
felsic, phaneritic
Vesicular
full of gas bubbles; frothy
intrusive
igneous rock that cold and solidify beneath the earths surface (inside the earth)
extrusive
igneous rock that cools and solidify on or above the earths surface
andesite
intermediate, aphanitic
Diorite
intermediate, phaneritic
which of the following best describes a porphyritic texture?
mineral grains different sizes, course and fine
Glassy
no crystals
which phaneritic igneous rock has the lowest silica content?
peridotite
volcanic
synonym for extrusive
How are igneous rocks classified?
texture: presence or absence of crystals composition: minerals or mineraloids present
pumice
volcanic glass, always felsic
