Kara StangleField assignment part 1

Metamorphic Rocks 1. Blueschist

For a metamorphic type I chose to find and talk about the rock blueschist. Blueschist is a metamorphic rock and how metamorphic rocks are formed is when there is when a rock undergoes change in pressure and also in temperature. When this happens the rock can or is exposed to shearing, stretching, or shortening. What is impressive and what I think is fascinating about this rock is that it is made by very immense pressure with relatively cool temperatures. I find this fascinating because the deeper that you go in to the earth the closer you get to the core so it gets hotter as you go down. But they are made with extremely high-pressure meaning that it is deep in the earth but is still cool. This happens to be because blueschist is found in subduction zones ware water can travel with the plate keeping rocks insulated from heat keeping them relatively cool.

Igneous rocksTo first explain igneous rock you would need to know that there are two different types of this rock intrusive and extrusive. Intrusive igneous rock is formed by the cooling of magma, which means that it is cooled below earth’s surface, and extrusive igneous rock is formed, by the cooling of lava, which is cooled on the surface of earth. Igneous rocks can be silicic, intermediate, mafic, and ultramafic. A few igneous rocks that I have collected are intrusive and were found in San Luis Obispo, on the trails of Bishops Peak and Mount Madonna. Decompression melting made these mountains. The Farallon Plate was separated from the Pacific Plate by a sea-floor spreading center.

Granite is an intrusive felsic igneous rock. Granite can be a pink grey color all depending on how this rock is composed. Granite is interesting because if you look at it close you can see the quarts in the rock shine and it consists of at least 2o percent of quarts. Granit I find interesting because on the west coast up to Canada there are huge batholiths, which are huge masses of granite. Along with finding some granite I also found what I think was gabbro and scoria

.Gabbro is also a intrusive igneous rock like that of granite I found these rocks on the same trail. Even though gabbro and granite are both intrusive igneous rocks their compounds of what they are made of is different. According to the book gabbro is the most abundant rock in the deep oceanic crust. I found this rock as I was running back down from the peak and noticed a dark rock with a shade of green and took it with me and looks like gabbro. Looking up gabbro I found out that it actually dose not have that much quarts in it at all which I thought was interesting because i believed that igneous rocks usually consist of a lot of quarts.

As for extrusive igneous rocks I believe that I found a rock called scoria. Scoria is different then the other rocks that I have just described in the igneous types because this rock is cooled on the surface rather then below it. The reasons that make me believe that this rock that I had found was scoria because of its dark reddish color and that it looks like it has areas of air pockets, and with scoria when it begins to harden there is gasses trapped in it, which causes these.

SEDIMENTARY ROCKS

As for sedimentary rocks the rock that I found and am going to describe to you is sandstone. Where I had found this rock was on a trail at Cal Poly SLO called Poly Canyon, which happens to have a lot of sandstone. According to the book “sedimentary rock forms either by the cementing together of fragments broken off preexisting rock or by the precipitation of mineral crystals out of water at or near the earths surface.” Sandstone is a clastic sedimentary rock which consists of a lot of quarts and sand that like explained above is cemented together.