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, biotite weathering 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 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
Obsidian Volcanic glass of the granite family. Cleavage or fracture? (conchoidal)
Rhyolite also in the granite family
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.
basalt Basalt is a fine-grained, dark-colored extrusive igneous rock composed mainly of plagioclase and pyroxene. Basalt is also abundant on the moon!
Gabbro is a coarse-grained, dark colored, intrusive igneous rock that contains feldspar, augite and sometimes olivine.
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 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.