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 Granite is much like ice cream.  Igneous dyke   Pumice  Clays are made up of feldspars from igneous rocks. | ||||
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RATINGS: Sites are rated from 1 owl (good) to a high of 5 owls. Read more- Why Is Feldspar so Important?
In addition to the fact that about 60% of Earth's crust is made of it, most igneous rocks are classified according to the kind and amount of feldspar they contain. This University of Oregon webpage provides a scheme for identifying feldspar and, therefore, igneous rock in the field.
- All Stone Is Not Alike
The choice of granite for making monuments is not arbitrary. Granite's attributes, most notably its resistance to weathering, make it particularly suited to the task. This Stone University website discusses the physical properties of a variety of stones from the standpoint of stone as building material.
- Earth's Rocks
Granite rock is a mixture of the minerals mica, hematite, and quartz. Granitic magma (molten rock), pretty heavy stuff, can be thrown into the air with the greatest of ease by volcanic explosions. In that case, even the sturdiest umbrella is of no help. This middle school webpage surveys rock formation and has a picture of erupting magma. Ruuun!
- Igneous Rock Identification
Magma rises from the asthenosphere (partially molten rock 60 to 100 kilometers below the surface) toward Earth's surface because it is less dense than the surrounding rock. As it rises, it begins to cool and eventually solidifies. Exactly how fast it does so determines its texture. And that, in part, is the key to classifying igneous rock. This university website introduces the classification scheme and the physical processes it is based on. Read through the page, then click on "I'm ready to identify IGNEOUS ROCKS" for some practice.
- Devil's Tower Geology
Devil's Tower, located in the state of Wyoming, is a column of igneous rock rising approximately 122 meters (400 feet) into the sky. Geologists agree it was formed by the intrusion of magma into a crack in the surrounding sedimentary rock. But exactly how it got its present shape is still a matter of debate. The Devil's Tower National Monument website explores the geology of the area and the processes that shaped the tower over the past 200 million years. And yes, this is the rock made famous by Steven Speilberg's movie, Close Encounters of the Third Kind.
- Types of Igneous Rocks
It all starts with igneous rocks as magma from Earth's interior rises to the surface and cools. Depending on how fast the magma cools and its composition will determine what type of igneous rock forms. Granite is created when magma is insulated within the crust, or intrusively. For granite, heat loss is at a minimum and minerals solidify slowly to produce larger crystals. An educational website details how igneous rocks form including a useful program that allows control of cooling rate and magma composition to see the resulting type of rock.
- Rocks
The type of igneous rock formed from molten rock depends on its rate of cooling, which in turn depends on its location of formation. This USGS webpage concisely summarizes the process, the rocks, and the terms which describe them. Intrude here for more information.
Igneous Rocks: Forged by Fire
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