Igneous Rocks Vocabulary
What is the most abundant component of Igneous rocks?
Silica
What is the texture of Obsidian?
glassy
What is the texture of Andesite?
porphyritic
What is the texture of Basalt?
porphyritic
Rock that has a spongy appearance due to trapped gas bubbles in the lava. texture (igneous)
Vesicular texture (igneous)
What is the finer grained rock adjacent to a contact with country rock called in an intrusion?
a chill zone
extrusive
fine-grained igneous rock that forms when magma cools quickly at or near Earth's surface
What is the texture of Pumice?
vesicular
What is the texture of Scoria?
vesicular
Intrusive texture
-Coarse grained-Large Crystals-Cooled Slowly -The longer the magma is allowed to cool the larger the crystals can be. -YOU CAN SEE THE INDIVIDUAL CRYSTALS.
What temperature does lava solidify for mafic rocks?
1,100 to 1,200 °C or 2,010 to 2,190 °F
What are the most important factors that influence viscosity?
1. the temperature of the lava relative to the cooler temperature at which it solidifies, 2. the silica (SiO2) content of the dissolved gas content, and 3. the gas content of the lava.
What is the common percent of silica found in mafic rocks?
45-55%
What part of the weight of a Igneous rock is typically silica?
45-75%
What percent of basalt is silica?
50%
What is the common percent of silica found in intermediate igneous rocks?
55-65%
What is the common percent of silica found in felsic igneous rocks?
65% and above
At what temperature does lava solidify for felsic rocks?
650o and 800o Celsius or 1202o and 1472o Fahrenheit
Approximately how hot is lava?
700 to 1,200 °C (1,300 to 2,200 °F)
What is the crater of a volcano?
A bowl shaped depression around the vent at the top of the volcano
What is a vesicle?
A cavity caused by gas in lava.
volcanic neck
A deposit of hardened magma in a volcano's pipe
What is a volcano?
A hill or mountain constructed by the extrusion of lava or rock fragments from a vent.
Viscosity
A liquid's resistance to flowing
laccolith
A massive igneous body intruded between preexisting strata
How big are blocks and bombs in a pyroclastic explosion?
A minimum of 2 inches.
What is a tuff?
A rock formed of fine-grained pyroclastic particles.
What is a volcanic Breccia?
A rock made up of large volcanic fragments like blocks and bombs.
dike
A slab of volcanic rock formed when magma forces itself across rock layers
How big are cinders?
About the size of sand grains.
porphyritic texture (igneous)
An igneous rock texture in which large crystals are scattered on a background of much smaller crystals.
Phaneritic (coarse-grained) texture
An igneous rock texture in which the crystals are roughly equal in size and large enough so the individual minerals can be identified without the aid of a microscope.
pyroclastic texture (fragmental)
An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption.
Plutonic
An igneous rock that solidified at a considerable depth underground. (large crystal size)
What is the vent on a volcano?
An opening in the crust from which lava erupts.
What are common intermediate igneous rocks?
Andesite (extrusive) and it's equivalent Diorite (intrusive), Syenite (intrusive).
A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished without the aid of a microscope.
Aphanitic texture (igneous)
What are some common mafic igneous rocks?
Basalt (extrusive) and it's equivalent Gabbro (intrusive), Scoria (extrusive).
Felsic
Describes magma or igneous rock that is rich in feldspars and silica and that is generally light in color.
What are the smallest particles in a volcanic explosion?
Dust and ash
What causes pillow basalts?
Elongate blobs of lava break out of a thin skin of basalt over the top of a flow that is submerged in water. Each blob is squeezed out like toothpaste, and its surface is chilled to rock almost instantly. A new blob forms as more lava inside breaks out. Each new pillow settles down on the pile, with little space left in between.
A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals.
Glassy texture (igneous)
Ultramafic
Igneous rocks with low silica content and very high levels of magnesium and iron. Periodite, dunites, and doirite are examples.
What are common ultramafic rocks?
Komatiite (extrusive) and it's equivalent Peridotite (intrusive).
What is porphyritic texture?
Larger mineral grains in a matrix of smaller grains (associated to intrusive or extrusive igneous rocks)
What percent of silica does a ultramafic igneous rock contain?
Less than 45%
What kind of lava makes up submarine eruptions, what rock is almost always formed?
Mafic lava, basalt.
What is lava?
Magma that reaches Earth's surface, also used for the solidified rock formed by the cooling of a molten lava flow.
What is magma?
Molten rock beneath the earth's surface that is mostly silica.
What is the chemical equivalent of rhyolite?
Obsidian
What are the large minerals in a porphyritic rock called?
Phenocrysts
What igneous rocks were formed by vast outpourings of lava in the geological past?
Plateau basalts
Igneous rock that formed at a great depth.
Plutonic rock
What igneous rocks are felsic?
Rhyolite (extrusive) and it's equivalent Granite (intrusive), Pumice (extrusive), Obsidian (extrusive).
pyroclastic flow
The expulsion of ash, cinders, bombs, and gases during an explosive volcanic eruption
What happens if lava has a high dissolved gas content?
The lava is more fluid.
What are the small crystals in a porphyritic rock called?
The matrix
Bowen's Reaction Series
The sequence in which different silicate minerals crystallize during the progressive cooling of a melt
What are some common characteristics of mafic lavas?
They are the least viscous and are associated with quiet eruptions.
What igneous rocks can range from intermediate to felsic?
Tuff (extrusive), Pegmatite (intrusive).
What does a porphyritic texture indicate about the history of an igneous rock?
Two stages of solidification. (Minerals that form at higher temperatures crystallize and form phenocrysts in the still partially fluid magma. if the entire mass is erupted, the remaining liquid cools quickly forming the fine-grained matrix.)
pyroclastic
What is the texture of tuff?
What is a fine-grained igneous rock?
When an igneous rock is comprised of mostly grains that are smaller than 1mm. In some cases individual minerals are only distinguishable with use of a microscope.
Fragment of rock distinct from the igneous rock in which it is enclosed.
Xenolith
sill
a slab of volcanic rock formed when magma squeezes between layers of rock
What is a contact?
a surface separating different rock types
pegmatitic texture
a texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter
What is the texture of Rhyolite?
aphanitic (fine grained)
What rock makes up the oceanic crust?
basalt and it's intrusive equivalent Gabbro.
What are pyroclastic rocks?
clastic rocks composed solely or primarily of volcanic materials
A structure that forms in rocks (most commonly in basalt) that consists of columns (mostly commonly hexagonal in shape) that are separated by joints or fractures in the rock that formed when the rock contracted, most often during cooling.
columnar jointing
Mafic
describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color
What is the most abundant intrusive igneous rock?
granite
batholith
large mass of intrusive igneous rock believed to have solidified deep within the earth
What is the texture of Diorite?
phaneritic (coarse grained)
What is the texture of Gabbro?
phaneritic (coarse grained)
What is the texture of Granite?
phaneritic (coarse grained)
What is the texture of Peridotite?
phaneritic (coarse grained)
What is the texture of Syenite?
phaneritic (medium to coarse grained)
What is the texture of Pegmatite?
phaneritic (variable texture and coarseness depending on specimen.)
What are lava flows?
streams of molten rock that pour or ooze from an erupting vent
What is another name for pyroclastic debris?
tephra
A rock's appearance with respect of size, shape, and arrangement of its grains or other constituents.
texture
lava flow
the area covered by lava as it pours out of a vent
