Igneous rocks form from magna. There are two distinct types.
Intrusive igneous rocks form before magma reaches the surface when it slows and crystallizes. Also called plutonic “after Pluto, the god of the lower world” these rocks usually stay below the surface unless enough erosion has occurred to expose them. 6
Extrusive Igneous Rocks form when lava hardens at the surface. Also know as volcanic “after the Roman fire god Vulcan” these rocks are more common in “western portions of the Americas.” 7
Igneous Rhyolite I believe this rock to be Rhyolite. Part of the Igneous family of rocks. Its texture is aphanitic or “fine grained” and it is a rosy/gray color. 8 Rhyolite is not as common as other forms of Igneous rock but occurs in areas where volcanoes are present. I am probably wrong but this is my best guess.
Igneous Andesite This rock looks to be andesite. It is “medium-gray, fine-grained” and also contains what look like black crystals. 9 Andesite is also commonly found around volcanoes located around the Pacific Ocean so again it makes sense that I would find this near Mt. Shasta.
Igneous Norite I had a hard time attempting to name this rock. It looks like a lot of different rocks and the texture is hardly telling. I think it looks most like Norite. Norite is a intrusive igneous rock meaning it is coarse grained and contains minerals which are visible on this rock in the light.
Sedimentary rocks are a collection of sentiment formed over time through a natural process.
Weathering is where it starts. Rocks that already exist are broken down into sediment. Then the sediment is carried away by “runoff and groundwater.” 10
The sediment then slows and settles forming layers.
There are different ways that sediment is transported and formed into “solid rocks” and that is why sedimentary rocks are broken down into three categories; detrital, chemical, and organic. 11
Sedimentary Conglomerate This is a really good clear example of conglomerate detrital sedimentary rock because it very obviously contains many other smaller rock particles. I think I found this and a few others like it at Mount Shasta because of the glacial activity there along with the occurrence of avalanches on the constantly snow capped mountain.
Metamorphic rocks always have a parent rock that can come from one of the three categories of rocks. Metamorphic “means to change form” and that is exactly how metamorphic rocks are formed and classified. 12 Metamorphism usually happens in 3 ways.
Thermal metamorphism is when a rock changes because of heat.
Hydrothermal metamorphism happens when a rock encounters chemical heat.
Regional metamorphism occurs when rocks “are subjected to the directed pressures and high temperatures associated with large-scale deformation.” 13
Metamorphic Schist To me this rock resembles schist. Schist is a type of metamorphic rock that is formed over time by “heat, pressure, or stress” and all of those things were surely happening up until the last 200 years on Mt. Shasta. 14
1 Tarbuck, E. J., & Lutgens, F. K. (2011). Earth: An introduction to physical geology. New Jersey: Pearson Prentice Hall. Pg. 151.
2 Mount Shasta Companion. (n.d.). Geology. Retrieved November 28, 2011, from http://www.siskiyous.edu/shasta/geo/his.htm