L> Basalt and also Granite ask GeoMan... What are the most important types of absent in the crust? excluding the rocks in between my ears, I"d have to say the basalt and also granite have actually the respect of gift the most important rocks in the crust. Basalt and granite actually have actually quite a bit in common. Both space igneous rocks, which method that they cooled native a magma (the planet gets really hot just below the surface, and also there is numerous liquid absent available). Both are made up of mineral from the silicate group, for this reason both have large amounts of silicon and oxygen. Both will hurt if girlfriend drop a large piece on your toe. However there space several necessary differences, too. These differences aid define and explain just how the planet works. Granite is great stuff! Not only is the my personal favorite, that is there is no a doubt the most usual rock kind on the continent land masses. Yosemite sink in the Sierra Nevada and Mt. Rushmore room two notable instances of granitic rocks. Yet granitic "basement rock" deserve to be found just about everywhere eastern of the Rockies if you"re willing to dig with the dirt and sedimentary rocks at the surface. Granite is intrusive, which method that the magma was trapped deep in the crust, and also probably take it a really long time come cool down enough to crystallize right into solid rock. This allows the mineral which form plenty the time to grow, and also results in a coarse-textured absent in which individual mineral seed are easily visible. Granite is the can be fried silicate rock. As discussed elsewhere in better detail, on typical oxygen and also silicon account because that 75% the the earth"s crust. The remaining 25% is split amongst several various other elements, with aluminum and potassium contributing the many to the formation of the continental granitic rocks. Fairly small amounts of iron and also magnesium occur, but due to the fact that they have actually generally higher densities it"s not surprising that there isn"t an extremely much in the granite. Because of the procedure of differentiation, many of the heavier aspects are moving towards the main point of the earth, permitting the silicon and oxygen come accumulate ~ above the surface. And also accumulate that has. Sufficient granitic "scum" has differentiated to the surface ar to sheathe 25% come 30% of the earth with the an excellent stuff. We call this purified material felsic since of the fairly high percentage of silica and oxygen. Basalt is extrusive. The magma native which the cools breaks through the tardy of the earth and erupts top top the surface. We call these varieties of occasions volcanic eruptions, and there space several key types. The volcanoes the make basalt are an extremely common, and also tend to form long and persistent zones of rifting in nearly every one of the ocean basins. Us now think that this undersea volcanic areas represent large spreading ridges wherein the earth"s crust is separating. It"s a lot prefer a reduced on your arm, which will certainly bleed till a scab forms. Basaltic magma is choose the blood of the earth - it"s what come out as soon as the earth"s skin is reduced the whole way through. Together an eruption ends, the basalt "scab" heals the wound in the crust, and the earth adds some brand-new seafloor crust. Since the magma comes out of the planet (and regularly into water) the cools really quickly, and also the minerals have very tiny opportunity come grow. Basalt is commonly very fine grained, and it is virtually impossible to view individual minerals without magnification. Basalt is taken into consideration a mafic silicate rock. Among other characteristics, mafic minerals and also rocks are normally dark in color and also high in details gravity. This is in big part as result of the lot of iron, magnesium, and also several other reasonably heavy elements which "contaminate" the silica and also oxygen. However this hefty stuff yes, really isn"t happy near the surface, and will take any opportunity it deserve to to head because that deeper levels. The trick is to warm the basalt ago up again so it deserve to melt and give the iron an additional shot in ~ the core. It desires to it is in there, and also heat is the key which unlocks the door. As it turns out, many of the ocean floor is basalt, and most of the continents room granite. Basaltic crust is dark and thin and also heavy, while granite is light and accumulates right into continent-sized rafts which bob around like corks in this "sea the basalt." once a continent runs right into a piece of seafloor, it"s lot like a Mac van running into a Volkswagon. Not an extremely pretty, yet at the very least there"s a clear winner. And the seafloor basalt ends up in pretty lot the same place as does the VW - under the truck (or continent, together the situation may be). This may seem like a traction for the basalt, yet remember that it isn"t all the happy top top the surface anyway, and this offers it the warm it needs to re-melt and shot to finish the differentiation process which was so rudely interrupted at the spreading ridge. If successful and permitted to continue, what"s left behind is a "purified" magma with many of the iron, magnesium, and also other heavy facets removed.

You are watching: Light-colored rocks with lower densities form from basaltic magma.

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Once it cools, guess what forms? and also the continent land massive just got a wee bit larger.