Igneous Rocks Quiz (Geo 101)
Intermediate igneous rock
Intermediate rocks fall somewhere in between being Felsic and Mafic.
Intrusive igneous rocks
Intrusive igneous rock: MAGMA cools off BENEATH the surface Phaneritic texture (coarse grained) SLOW COOLING
Rock Texture: Phaneritic
Coarse grained Intrusive (all others extrusive) Igneous rocks with crystals that are visible to the unaided eye.
Differing mineral COMPOSITIONS of igneous rocks
Composition of igneous rocks is controlled by the plate tectonic environment and is dependent on the mineral make up. 1. Felsic (white, pink rocks) --> light colored minerals (Quartz, Feldspars, Plag) 2. Intermediate (A mixture of light and dark, dark green sometimes e.g. Plag, Amphibole) 3. Mafic (Dark minerals e.g. Amphibole & Pyroxene) 4. Ultramafic (dark minerals e.g. Pyroxene & Olivine)
Felsic magmas are more ______________ due to a higher viscosity and volatiles
Felsic magmas are more EXPLOSIVE due to a higher viscosity and volatiles
Felsic igneous rock
Felsic rocks are those that are light in color and are mostly made up of feldspars and silicates.
Rock Texture: Aphanitic
Fine grained, minerals are too small to see. Extrusive (SUGAR cookie) Do not have crystals that can be seen with the unaided eye because magma solidifies too rapidly.
Coarse grained
Form at greater depths where the magma cools at a slow rate that allows large crystals to grow. Crystals can be seen with a unaided eye.
Fine grained
Form if magma only has enough time to grow small crystals. Occurs when magma solidifies on the surface in a thick lava flow or at shallow depths beneath the surface because cooling in these settings is fairly rapid. Has crystals that are to small to see with the unaided eye
Rock Texture: Pyroclastic
Fragmented rock composed of ash, lithics, and crystal grains. Extrusive When molten material is erupted from a volcano it can solidify before it hits the ground, yet still be hot enough to weld to other erupted material. This forms a rock called tuff, which is composed of fragments ( of other rocks) and crystals, all embedded in a matrix of ash.
Rock Texture: Vesicular
Gas bubbles, holes. Extrusive Form when gasses dissolved in magma accumulate to bubbles. Holes in volcanic rocks that form as lava solidifies around gas bubbles.
What is the difference in composition between Felsic, Intermediate, Mafic, and Ultramafic igneous rocks?
Igneous rocks contain the following common minerals: Plagioclase feldspar, Olivine, Potassium feldspar, Pyroxene, Quartz, Amphibole, Biotite, and Muscovite.
Mafic ingeous rock
Mafic rocks are darker colored and are mostly made up of magnesium and iron.
Extrusive igneous rocks
Magma comes out as LAVA and COOLS ON THE surface Many textures COOLS FAST
Rock Texture: Glassy
No crystal structure. Extrusive
Oceanic crust is composed of _____________________ minerals. Continental crust is composed of _____________ minerals. Name one of each mineral above.
OCEANIC crust is composed of MAFIC minerals. CONTINENTAL crust is composed of FELSIC minerals. One FELSIC mineral: GRANITE One INTERMEDIATE mineral: ANDESITE One MAFIC mineral: BASALT
Rhyolite
Texture: APHANITIC Composition: FELSIC Intrusive/Extrusive?: EXTRUSIVE LIGHT COLORED (usually PINKish)
Andesite
Texture: APHANITIC Composition: INTERMEDIATE Intrusive/Extrusive?: EXTRUSIVE
Basalt
Texture: APHANITIC Composition: MAFIC Intrusive/Extrusive?: EXTRUSIVE
Obsidian
Texture: GLASSY Composition: MAFIC to FELSIC Intrusive/Extrusive?: EXTRUSIVE Rock will look like glass & Be BLACK in color
Granite
Texture: PHANERITIC Composition: FELSIC Instrusive/Extrusive?: INTRUSIVE Speckled coarse grained rock (looks like a kitchen counter)
Diorite
Texture: PHANERITIC Composition: INTERMEDIATE Intrusive/Extrusive?: INSTRUSIVE Similar to granite but DARKER Usually has BLACK CRYSTALS (Amphibole) but are LARGER and there is MORE OF THEM than what is found in granite.
Gabbro
Texture: PHANERITIC Composition: MAFIC Intrusive/Extrusive?: INTRUSIVE BLACK rock containing CRYSTALS, COARSE GRAINED
Porphyritic Andesite
Texture: PORPHYRITIC Composition: INTERMEDIATE Intrusive/Extrusive?: EXTRUSIVE
Volcanic Tuff
Texture: PRYOCLASTIC (fragmented rock) Composition: MAFIC to FELSIC Intrusive/Extrusive?: EXTRUSIVE LIGHT weight, mostly composed of ASH
Pumice
Texture: VESICULAR Composition: FELSIC Intrusive/Extrusive?: EXTRUSIVE LIGHT WEIGHT Made of ASH
Vesicular Basalt
Texture: VESICULAR Composition: MAFIC Intrusive/Extrusive?: EXTRUSIVE DARK GREY rock with GAS BUBBLES that is HEAVY
Scoria
Texture: VESICULAR Composition: MAFIC Intrusive/Extrusive?: EXTRUSIVE DARK RED or BLACK in color, Has HOLES that are usually BIGGER than those in Pumice
Where are igneous rocks found?
The most common igneous rock Basalt (mafic) makes up most of the OCEANIC plates and is founds at divergent plate boundaries. In fact most igneous rock activity occurs at divergent plate boundaries. However, intermediate to felsic igneous rocks are most commonly found along CONTINENTAL margins.
Bowen's Reaction Series
The order in which minerals crystallize: Highest Temp 1400 degrees CELSIUS: First to crystallize (1) OLIVINE (crystallizes first/melts last) (2) PYROXENE (3) AMPHIBOLE (4) BIOTITE (5) FELDSPAR (6) MUSCOVITE (7) QUARTZ (crystallizes last/melts first) Lowest Temp 450 degrees CELSIUS: Last to crystallize
Igneous Rock
The product of cooled solidified magma/lava. As magma/lava cools it goes through the process of crystallization which turns it into an igneous rock. The amount of time it takes for an igneous rock to form depends on its LOCATION and its COMPOSITION.
Ultramafic ingeous rock
Ultramafic rocks are very dark colored.
Volatiles are ______________. The two most common ones are ____________ and ______________. Volatiles are usually found in _____________________________
Volatiles are GASSES. 2 most common: WATER & CARBON DIOXIDE. Usually found in MELTS WITH HYDROUS MINERALS
Rock Texture: Porphyritic
large grains in a fine grain ground mass, Extrusive (CHOCOLATE CHIP cookie) Mixture of fine-grained and coarse grained. Needs sufficient time in a subsurface magma chamber to grow visible crystals.
