Igneous Rock week

This week in class we took our tests and recieved the results on wednesday.  I feel the test was very in par with the material we went over in class and that I was very well prepared for it.  Looking over the test I feel that I could have spent a little more time memorizing specific stuff such as the principles for rock formation.  My mind blanked when it came to naming five of them and after I got the first three, I forgot the names of the last two, even though I knew the principle itself. 

The new material we began is igneous rocks.  We have learned the basics of magma chambers and volcanoe activity.  Also, we have got to see examples of different types of rock that form based on their rate of cooling.  For example, we learned that if a rock that forms under the surface cools very fast, it is unable to produce crystals and gives off a glassy luster.  However, if a rock cools slowly, then it will form those crystals and you will be able to see them in the rock.  The slow cooling rocks are called phaneritic, the fast cooling rocks are called aphanitic, and rocks that cool slow at first and then cool fast so that the result is a glassy rock with crystals are called porphyritic rocks.  We learned the difference between felsic and mafic materials.  Felsic lava is slow moving and very dense so that it may cause violent erruptions because the slow movement creates the inability for gas to escape.  Mafic lava flows more quickly and is relatively thin, almost like a light syrup.  Felsic material forms at a cooler temperatur than mafic and is also a lighter color than mafic.  This is because mafic material tends to have more iron in it while felsic material has more silica. When material melts in the mantle, it will be mafic magma, but if it melts in the continental crust, it will be felsic.  When dealing with this material, the melting point occurs at the point where the temperature can overcome the pressure. 

The most important topic we covered this week was when we took a look at Bowen’s reaction series.  This chart shows that as material forms at cooler temperatures, it goes from mafic material to intermediate material to felsic material.  It will also change in mineral composition too.  The top mineral is Olivine, and then it goes down to Quartz with Hornblend, Pyroxene, Biotite, Feldspare, and Muscovite in between. Furthermore, the top minerals of the chart tend to be more Calcium rich and as you move down they become more Sodium rich. 

An interesting article I read this week was about Samson the T-Rex.  Samson is a T-Rex skeleton that is considered the third most complete T-Rex skeleton in the world.  They tried to sell it in Las Vegas this week with an estimated going rate of 8 million, which is what a similar fossil sold for a few years ago.  However, the bidding stoped short of 4 million.

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