What Family Do Granite and Basalt Belong to
Ask GeoMan...
What are the most important types of stone in the crust?
Excluding the rocks between my ears, I'd have to say that basalt and granite accept the honor of being the virtually important rocks in the crust.
Basalt and granite really accept quite a bit in common. Both are igneous rocks, which means that they cooled from a magma (the earth gets very hot just beneath the surface, and there is lots of liquid rock bachelor). Both are made up of minerals from the silicate group, so both have large amounts of silicon and oxygen. Both will hurt if you drop a big piece on your toe. Only there are several important differences, too. These differences help define and explain how the earth works.
Granite is dandy stuff! Not only is it my personal favorite, it is without a doubt the nigh common rock blazon on the continental land masses. Yosemite Valley in the Sierra Nevada and Mt. Rushmore are two notable examples of granitic rocks. But granitic "basement stone" can be found just almost everywhere eastward of the Rockies if y'all're willing to dig through the dirt and sedimentary rocks at the surface. Granite is intrusive, which means that the magma was trapped deep in the chaff, and probably took a very long time to cool down enough to crystallize into solid rock. This allows the minerals which form enough of time to grow, and results in a coarse-textured rock in which individual mineral grains are easily visible.
Granite is the ultimate silicate rock. As discussed elsewhere in greater detail, on average oxygen and silicon account for 75% of the earth's crust. The remaining 25% is split among several other elements, with aluminum and potassium contributing the most to the formation of the continental granitic rocks. Relatively modest amounts of iron and magnesium occur, but since they have generally higher densities it's not surprising that in that location isn't very much in the granite. Due to the process of differentiation, most of the heavier elements are moving towards the core of the earth, allowing the silicon and oxygen to accumulate on the surface. And accumulate information technology has. Enough granitic "scum" has differentiated to the surface to encompass 25% to 30% of the earth with the good stuff. We call this purified textile felsic because of the relatively high percentage of silica and oxygen.
Basalt is extrusive. The magma from which it cools breaks through the chaff of the earth and erupts on the surface. We call these types of events volcanic eruptions, and in that location are several main types. The volcanoes that brand basalt are very mutual, and tend to course long and persistent zones of rifting in nearly all of the ocean basins. Nosotros now believe that these undersea volcanic areas represent huge spreading ridges where the earth's crust is separating. Information technology's a lot like a cut on your arm, which volition bleed until a scab forms. Basaltic magma is like the claret of the earth - it's what comes out when the earth's pare is cutting the whole way through. Every bit an eruption ends, the basalt "scab" heals the wound in the chaff, and the earth adds some new seafloor crust. Because the magma comes out of the earth (and often into water) information technology cools very chop-chop, and the minerals have very trivial opportunity to grow. Basalt is commonly very fine grained, and it is virtually impossible to encounter individual minerals without magnification.
Basalt is considered a mafic silicate stone. Among other characteristics, mafic minerals and rocks are generally night in color and high in specific gravity. This is in big part due to the amount of fe, magnesium, and several other relatively heavy elements which "contaminate" the silica and oxygen. But this heavy stuff actually isn't happy near the surface, and will have any opportunity it can to head for deeper levels. The fob is to heat the basalt back up once again and then it tin cook and give the fe another shot at the core. It wants to be there, and heat is the key which unlocks the door.
Equally information technology turns out, most of the bounding main flooring is basalt, and most of the continents are granite. Basaltic crust is nighttime and thin and heavy, while granite is calorie-free and accumulates into continent-sized rafts which bob well-nigh like corks in this "sea of basalt." When a continent runs into a slice of seafloor, it's much similar a Mac truck running into a Volkswagon. Not very pretty, just at to the lowest degree there's a articulate winner. And the seafloor basalt ends up in pretty much the same position as does the VW - nether the truck (or continent, as the case may be). This may seem similar a drag for the basalt, but remember that it isn't all that happy on the surface anyhow, and this gives information technology the oestrus it needs to re-melt and try to complete the differentiation procedure which was so rudely interrupted at the spreading ridge. If successful and immune to continue, what's left behind is a "purified" magma with most of the iron, magnesium, and other heavy elements removed. When it cools, guess what forms? And the continental land mass simply got a wee bit larger.
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since April 1, 1997 Source: http://jersey.uoregon.edu/~mstrick/AskGeoMan/geoQuerry27.html
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