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Granite

Granite is a great example of a silicate rock. It is a common and well recognized terrestrial rock, from Yosemite's El Capitan, to boulders making up a typical rocky fence, to a fancy bathroom countertop.

Granite is made up of a mixture of minerals comprised of about 60% orthoclase and plagioclase feldspars, about 25% quartz and about 5% darker minerals of which biotite and horneblende are examples. The dominant feldspar usually gives granite a flesh color, but other colors exist, including grey and white with black crystals intermingled.

Granite is usually formed in a magma chamber, under the phenomena known as solid solution. In this phenomena, the dark minerals crystallized first. Being still surrounded by molten matter, and in fact, dissolved in it, they were free to grow into beautiful crystalline forms. The orthoclase then began to crystallize, but under somewhat more constricted conditions, so the crystals are not quite so perfect. Finally, the quartz crystalized into whatever space remained in the now nearly solid rock. Its crystals, therefore, were much more irregular in form, developing into an interlocking arrangement with other mineral crystals. This gave the granite not only its granular structure but the rigidity and toughness for which it is noted.

In time the rock will erode away and the various pieces will be deposited and resolidify as sedimentary rock. Or, there will be some new surface process which will crush the rock under pressure and perhaps an accompanying temperature increase, leading to metamorphism.


This image shows a type of igneous rock called granite.
Click on image for full size version (92K JPG)
Image from: C. Alexander

Go to a listing of Rocks by mineral group


Granite

Granite is a great example of a silicate rock. It is a common and well recognized rock, from Yosemite's El Capitan, to boulders making up a typical rocky fence, to a fancy bathroom countertop.

Granite is made up of a mixture of minerals comprised of about 60% orthoclase and plagioclase feldspars, about 25% quartz and about 5% darker minerals of which biotite and horneblende are examples. The dominant feldspar usually gives granite a flesh color, but other colors exist, including grey and white with black crystals intermingled.

Granite is usually formed in a magma chamber, under the process known as solid solution. In this process, the dark minerals crystallize first. Being still surrounded by molten matter, and in fact, dissolved in it, they are free to grow into beautiful crystalline forms. The orthoclase then crystallizes, but under somewhat more constricted conditions, so the crystals are not quite so perfect. Finally, the quartz crystalizes into whatever space remained in the now nearly solid rock. Its crystals, therefore, are much more irregular in form, developing into an interlocking arrangement with other mineral crystals. This gives the granite not only its granular structure but the rigidity and toughness for which it is noted.

In time the rock will erode away and the various pieces will be deposited and resolidify as sedimentary rock. Or, there will be some new surface process which will crush the rock under pressure and perhaps an accompanying temperature increase, leading to metamorphism.


This image shows a type of igneous rock called granite.
Click on image for full size version (92K JPG)
Image from: C. Alexander

Go to a listing of Rocks by mineral group


Granite

Granite is a great example of a silicate rock. It is a common and well recognized rock, from Yosemite's El Capitan, to boulders making up a typical rocky fence, to a fancy bathroom countertop.

Granite is made up of a mixture of minerals. The dominant mineral, feldspar, usually gives granite a flesh color, but other colors exist, including grey and white with black crystals intermingled. In fact, when the sun sets at Yosemite Valley, El Capitan can appear to be quite pink.

Granite is usually formed in a magma chamber. In this process, the dark minerals crystallize first. Being still surrounded by molten matter, and in fact, dissolved in it, they are free to grow into beautiful crystalline forms. The next mineral then crystallizes, but under somewhat more constricted conditions, so the crystals are not quite so perfect. Finally, the last minerals crystallize into whatever space remained in the now nearly solid rock. Its crystals, therefore, are much more irregular in form, developing into an interlocking arrangement with other mineral crystals. This gives the granite not only its granular structure but the rigidity and toughness for which it is noted.

In time the rock will erode away and the various pieces may resolidify as sedimentary rock. Or, there will be some surface process which will crush the rock under pressure and perhaps an accompanying temperature increase, leading to metamorphism.


This image shows a type of igneous rock called granite.
Click on image for full size version (92K JPG)
Image from: C. Alexander

Go to a listing of Rocks by mineral group



Last modified January 15, 1998 by the Windows Team

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