(MODULE 3) ROCK CYCLE & IGNEOUS ROCKS Flashcards
How are igneous rocks formed?
magma cools over time and solidifies. This process called crystallization occurs either beneath the surface or at the surface following a volcanic eruption. The resulting rocks are called igneous rocks.
igneous rocks which form when magma erupts at the surface and rapidly cools.
Extrusive igneous rocks
extrusive igneous rocks are also called ___.
volcanic rocks.
igneous rocks which form when magma intrudes into bedrock and slowly cools.
intrusive igneous rocls
intrusive igneous rocks are also called ___.
plutonic rocks
igneous rocks are composed mainly of ___
silicate minerals
Igneous rocks composed almost entirely of light-colored silicates like quartz and potassium feldspar belong to the ___ group and is described to have ___ composition.
granitic or felsic
Rocks that contain at least 45 percent dark silicate minerals and calcium-rich plagioclase feldspar (but no quartz) are said to have a ___ composition.
basaltic
Basaltic rocks contain a high percentage of ferromagnesian minerals, so geologists also refer to them as ___.
mafic
This important category of igneous rocks is often associated with volcanic activity that is typically confined to the seaward margins of the continents and on volcanic island arcs such as the Aleutian chain.
andesitic
rocks composed entirely of ferromagnesian minerals
ultramafic
where is ultramafic rock often found?
upper mantle
types of igneous texture:
1.
2.
3.
4.
5.
6.
7.
- glassy
- porphyritic
- phaneritic (course-grained)
- vesicular
- pyroclastic (fragmental)
- aphanitic (fine-grained)
- pegmatitic
When molten rock is ejected into the atmosphere during eruptions, rapid cooling will cause the ions to solidify before forming a crystalline structure, resulting in a ___.
glassy texture
If molten rock containing large crystals undergoes a change in environment, the resulting rock which has large crystals embedded in a matrix of smaller crystals has a ___.
porphyritic texture
The large crystals in porphyritic rocks are referred to as ___, whereas the matrix of smaller crystals is called ___. A rock with a porphyritic texture is termed a ___.
- phenocrysts
- groundmass
- porphyry
When large masses of magma slowly crystallize at great depth, they form igneous rocks that exhibit a coarse-grained texture described as ___.
The course-grained rocks are large enough to be identified without a microscope.
phaneritic
Common features of many extrusive rocks are the voids left by gas bubbles that escape as lava solidifies. These nearly spherical openings are called ___, and the rocks that contain them are said to have a ___ texture.
- vesicles
- vesicular texture
igneous rocks formed from the consolidation of individual rock fragments ejected during explosive volcanic eruptions have a ___ texture.
pyroclastic or fragmental
Igneous rocks that form at the surface or as small intrusive masses within the upper crust where cooling is relatively rapid exhibit a fine-grained texture termed ___.
the fine-grained rocks has to be distinguished with a microscope
aphanitic
best known igneous rock
granite
dark-colored glassy rock
obsidian
these rocks occur as small masses or thin veins within or around the margins of large intrusive igneous bodies, and form late in the crystallization of a magma.
such rocks have a ___ texture.
pegmatitic
factors that influence the texture of igneous rock
1.
2.
3.
- rate at which molten rock cools
- amount of silica present in magma
- amount of dissolved gases in magma
a polymorph of diamond
graphite
another term for silica rich rocks found in the continental crust
felsic
silica-deficient rocks found in the oceanic crust
mafic
