Geology 1 Field Assignment- Part 1

Maria Diaz

I was walking down by the railroad tracks along the side of the canal on one evening and as I walked and walked I realized that there were many different types of rocks laying there near the tracks. These tracks are located in the side of the small town of Firebaugh that I live in. This small community is located northwest of Fresno off Highway 33. Incorporated in 1914, Firebaugh has grown from ferry crossing to a small agriculture based city. Before the railroad, the San Joaquin River was the major thoroughfare to upstream communities. The ferry, located in Firebaugh, was the major crossing for prospectors heading for gold country. Ferries were the only way to cross the river until the late 1800's when the first bridges were built. The San Joaquin River played a major role in the settling of the valley and Firebaugh is one of the oldest historical towns on the Westside. There was a variety of rocks so therefore I remembered that for this class I was to collect and identify five different rock samples. So here is where I gathered all my rock samples. To be honest I do not know how these rocks ended up being here but the least thing that I can think of was that when they were building the tracks people just came and dumped them here for a purpose. But one thing that I did learn about the history of this place is that there once existed water here. This was covered up by water many years ago.

This is the first sample that I picked up. I think that this rock belongs to the igneous group. Granite is the actual name of this rock. After doing research and after reading the chapter about igneous rocks I learned that this rock forms when cooling pockets of magma is trapped beneath the earth’s surface. This type of rock is usually used for long lasting monuments and for trim and decoration buildings. Granite is a coarse-grained rock that is composed of about 25 percent quartz and 65 percent of feldspar. Granite also consists of quartz crystals, which are roughly spherical in shape and are often glassy and clear to light gray in color. This rock’s texture phaneritic.

I categorized my second sample in the metamorphic group. This rock is marble. Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone. Marble is composed primary of calcium carbonate. This rock is pure white. These rocks are used to create monuments and statues. Its composition of calcium carbonate cause it to weather when exposed to acid rain. The texture is smooth at some angles and very sharp at others. This rock is shinny when put under direct light.

My third sample is from the igneous group. This rock contains a vesicular texture. These types of rocks are full of bubbles. It indicates that it is a volcanic rock. Scoria is a lightweight extrusive rock. This rock has very distinctive gas bubbles and a darker color compared to pumice. This rock is considered a product of basaltic low silica lavas than of felsic high-silica lavas. This is due to basalt usually being more fluid than felsite, which allows bubbles to grow larger before it freezes. This forms as the crust on lava flows that crumbles off as the flow moves. Eruptions can cause it to be blown out of the crater. This texture usually has broken connected bubbles and does not float in water.

This rock sample belongs to the sedimentary group. Sedimentary rocks are formed in places where water once existed in the area. This rock has many layers and that is why you can see many streaks of different colors. Some of these rocks contain fossils and other clues about the geologic past.

 My last and final sample belongs in the igneous group. This is a diorite. Diorite is a coarse grained igneous rock. This is considered an extrusive rock. The texture of this rock is pretty rough all around. This rock has shinny little particles. The texture of this is small grained texture from small crystal size. It has a black and white color to it. The black parts are amphibole and the light areas are made out of feldspar grains.