GEOLOGY 1Lab Assignment Part 1

Melinda WhitemanFall 2010

My first two samples were collected at Rosario Beach, at Deception Pass State Park in WA. The area at first appeared to have extruded igneous rock but upon closer examination the samples turned out to be sedimentary. This is an area that is not only wet but freezes, contributing to some major mechanical weathering. It is located in the Puget Sound almost directly east of Victoria, BC and the beach itself is along the edge of a mini-peninsula with a large outcropping in the middle. The samples are about 150-250 million years old from the Jurassic period.

Sample 1 - Sedimentary

I unwedged this first sample from a large, weathered area of rock on the beach. I believe it to be the sedimentary rock chert. There is a lot of quartz in it, especially the nice streak in the top picture. The rock itself isn’t nearly so green as it looks in the pictures – because it is only on the outside and not in the recently-broken area, I believe the green is more organic and not part of the composition of the rock itself.

Sample 2 - Sedimentary

It took some willpower not to try to “skip” this rock over the water! I believe it is the sedimentary rock shale. It is extremely fine-grained and while it’s been smoothed and rounded out, it seems like it would to want to break in layers (I didn’t have a good way to try to break it.) Also, Rosario Beach has tide pools and I found this near one, implying a relatively calm sedimentary environment for it to accumulate such fine grains.

My other three samples were collected in Fall City, WA, along the Snoqualmie River. The area’s volcanic rock was recently discovered to be 20 million years old (Miocene Epoch), and some of the other rocks

along the water appear to be metamorphic, leading me to believe they may be a bit younger than the igneous ones: perhaps later Miocene or

even Pliocene Epoch. This particular area just at the bottom of the pass; still elevated but the land here has flattened out quite a bit. The

rocks are likely from higher elevations and transported by the river.

Sample 3 - Igneous

This sample appears to be the igneous felsic rock granite. There is a lot of quartz (it sparkles, though you can’t tell so much in the picture) and pinkish feldspar, along with plenty of dark spots consisting of various other silicates.

Sample 4 - Igneous

At first glance I thought this rock may be sedimentary, but now I think it is actually the igneous rock andesite. It has a porphyrictic texture, some larger pieces among the otherwise fine-grained rock. I also felt that it was likely igneous due to the volcanic area I found it in.

Sample 5 - Metamorphic

This one had me nearly stumped! After quite a bit of researching I think it may be metamorphic – hornfels. It looks like quite a bit of pictures online and hornfels can be made of many materials that are then “baked.” The one thing that throws me off is that while this rock is very hard (as are hornfels) it is broken. It had to have already been broken because I only bumped it with my foot, which is how I found it, but I was very excited to get to pick up the pieces together and see the cleavage.

I honestly thought the rock identification would be much easier than it was. I’m hope I’m not too far off on any of my identifications, as I used both the book and quite a few sites and

searches. While this portion of the project was challenging, I can still honestly say that I think: