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Post on 16-May-2015
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Igneous rocks pt. 3
Some minerals that make up rocks
feldspar
Very common in the earth’s crust.
feldspar
biotite
hornblende
olivine
plagioclase
granite
granite
rock type: igneous
distinguishing features: completely crystallized, large, well formed interlocking crystals visible to the naked eye, no preferred crystal orientation, fairly light in color (white, gray, pink).
main minerals quartz, feldspar, biotiteweathering behavior : physical weathering can
break the rock along its crystal boundaries
granite is an igneous rock that forms by slow cooling of silica-rich magma deep within the earth
basalt
basalt
Basalt is an igneous rock that forms through rapid cooling at the surface of the earth. The island of hawaii, for example is almost entirely made from basaltic lava flows.
weathering of iron minerals can turn the surface tan or reddish brown (see image below
basalt
Obsidian
Volcanic glass of the granite family. Cleavage or fracture? (conchoidal)
Rhyolite
also in the granite family
rhyolite
rhyolite
Rhyolite is a light-colored, fine-grained, extrusive igneous rock that typically contains quartz and feldspar minerals.
So what makes a granite rock?
Rocks are made of minerals.
Granite rocks are made of quartz, feldspar, and at least one other mineral.
pumice
basalt
Basalt is a fine-grained, dark-colored extrusive igneous rock composed mainly of plagioclase and pyroxene.
Basalt is also abundant on the moon!
basalt
gabbro
Gabbro is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine.
diorite
diorite
Diorite is a coarse-grained, intrusive igneous rock that contains a mixture of feldspar, pyroxene, hornblende and sometimes quartz.
PORPHYRITIC ROCKS
Extrusive AND intrusive!
Porphyritic rocks
Rocks that have two distinctly different textures: large crystals AND fine-grained crystals.
Porphyritic rock
Porphyritic rocks
A theory of how porphyritic rocks are formed:
Magma cools slowly deep inside the earth. Large crystals are able to form.
THEN, the remaining liquid magma is pushed upward until close to the surface of the earth.
Forms fine crystals.
Porphyritic rock
Porphyritic granite
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