Obsidian
Igneous rocks are rocks that form by the cooling and solidification of magma.
Igneous rocks are classified according to their texture and composition.
Composition: mafic, intermediate, felsic
mafic: Iron and magnesium rich (Fe-Mg) Examples: basalt, gabbro, scoria
intermediate: equal amounts of Fe-Mg and Si Examples: Diorite, andesite
felsic: silica rich (Si) Examples: granite, rhyolite, pumice, obsidian
Texture: volcanic, plutonic, vesicular, glassy
Volcanic or extrusive igneous rocks are formed by the extrusion and cooling magma at the Earth's surface. They are recognized by an absence of visible crystals throughout the the rock. *Another term for absence of visible crystals is aphanitic (a = not, phaner = visible) . Examples include: basalt, andesite, rhyolite,and obsidian
Plutonic or intrusive igneous rocks are formed by the cooling and solidification of magma beneath the surface. They are recognized by the prescence of visible crystals throughout the rock due to slow cooling. * Another term for visisible crystals is phaneritic (phaner = visible). Examples: peridotite, gabbro, diorite, granite
Vesicular or frothy volcanic igneous rocks are formed by the extrusion of magma to the surface. the vesicles or cavities are gas bubbles in the magma. . The texture is often found in scoria and pumice.
Glassy texture results from cooling that was so extremely fast that no crystals could form, usually seen in obsidian. it contains no minerals and is usually black.
For more information please visit:
http://geology.com/rocks/igneous-rocks.shtml
For information on magmatic differentiation, origin of magma, areas of magma generation and crystallization please visit:
http://itc.gsw.edu/faculty/tweiland/igneous.htm
Video on igneous rocks:
http://www.videojug.com/film/geology-sedimentary-rocks
Igneous rocks are classified according to their texture and composition.
Composition: mafic, intermediate, felsic
mafic: Iron and magnesium rich (Fe-Mg) Examples: basalt, gabbro, scoria
intermediate: equal amounts of Fe-Mg and Si Examples: Diorite, andesite
felsic: silica rich (Si) Examples: granite, rhyolite, pumice, obsidian
Texture: volcanic, plutonic, vesicular, glassy
Volcanic or extrusive igneous rocks are formed by the extrusion and cooling magma at the Earth's surface. They are recognized by an absence of visible crystals throughout the the rock. *Another term for absence of visible crystals is aphanitic (a = not, phaner = visible) . Examples include: basalt, andesite, rhyolite,and obsidian
Plutonic or intrusive igneous rocks are formed by the cooling and solidification of magma beneath the surface. They are recognized by the prescence of visible crystals throughout the rock due to slow cooling. * Another term for visisible crystals is phaneritic (phaner = visible). Examples: peridotite, gabbro, diorite, granite
Vesicular or frothy volcanic igneous rocks are formed by the extrusion of magma to the surface. the vesicles or cavities are gas bubbles in the magma. . The texture is often found in scoria and pumice.
Glassy texture results from cooling that was so extremely fast that no crystals could form, usually seen in obsidian. it contains no minerals and is usually black.
For more information please visit:
http://geology.com/rocks/igneous-rocks.shtml
For information on magmatic differentiation, origin of magma, areas of magma generation and crystallization please visit:
http://itc.gsw.edu/faculty/tweiland/igneous.htm
Video on igneous rocks:
http://www.videojug.com/film/geology-sedimentary-rocks