Geology Field / Lab Assignment

By Lisa Nesgis

December 4, 2011

PART I

• California is an ideal place to observe many different types or rocks and offers a wide range of geological specimens.

• I was a little hesitant at first to try and determine where I could find these different types of rocks. Once I observed some geological maps of California online and researched my surrounding area, it didn’t take me long to discover that these rocks can be found in a number of different places and we don’t even know it.

• It takes a good understanding on California’s geological history to complete this field observation.

• The process I used in order to figure out rock types I collected was similar to that of a scientist. Question, research, hypothesize, test, analyze and conclude. With this formula I was able to accurately determine what type the collected rocks were.

Igneous rocks are formed from the solidification and cooling of molten rock material. There are two basic types: 1)intrusive igneous rocks such as diorite, gabbro, granite and pegmatite that solidify below Earth's surface; and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above 

Type of Rocks

What is an Igneous Rock?

The first rock to the left is Granite an example of intrusive igneous rock and the one to the right is Andesite and example of

extrusive igneous rocks.  

Igneous Rocks

InformationI got both of my igneous rocks at the famous Yosemite National Park. I found both of them in different parts of the park but it wasn’t till later I realized that only one of them was granite and the other was andesite. Most of Yosemite park is full of different rock types but mainly granite. I knew right away that both were igneous rocks from previous research and knowledge so it was an easy observation. After careful review and at home I figured out my hypothesis were correct. Below is a picture of the famous park where I located both these magnificent finds.

Metamorphic Rocks

Metamorphic rocks have been modified by heat, pressure and chemical process usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks. There are two basic types of metamorphic rocks: 1) foliated metamorphic rocks such as gneiss, phyllite, schist and slate which have a layered or banded appearance that is produced by exposure to heat and directed pressure; and, 2) non-foliated metamorphic rocks such as marble and quartzite which do not have a layered or banded appearance.  

Type of Rocks

What is a Metamorphic Rock?

These rocks that I collected were all examples of foliated metamorphic rocks. I believe the one on the right is Phyllite and

the other two on the left are Gneiss.  

Information I found this type of metamorphic rock at a random place along the

highway. When I was driving down south to visit my daughter. I happened to see a small boulder on the side of the road at the bottom of a mountain and had to take a look. I had a feeling that the rock I had came across was Gneiss. It was rough, and was layered with different but similar colors. I took a picture of the boulder but also found a small piece next to it. Out of all the rocks I enjoyed observing this one the most because of its appearance and appealing color change. I found the other metamorphic rock outside my parents house in the country where there is a lot of dirt and rocks. I came across this type of rock and of course it caught my eye because of its color and texture. After further investigation I concluded that it was indeed Phyllite.

Sedimentary Rocks

Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks: 1) clastic sedimentary rocks such as breccia, conglomerate, sandstone and shale, that are formed from mechanical weathering debris; 2) chemical sedimentary rocks such as rock salt and some limestones, that form when dissolved materials precipitate from solution; and, 3)organic sedimentary rocks such as coal and some limestones which form from the accumulation of plant or animal debris.

Type of Rocks

What is a Sedimentary Rock?

The rocks that I collected are examples of classic sedimentary rock. The rock on the right is conglomerate and the rock on the left is siltstone.

Information The second to last rock I came across or I should say came across

me is an example of sedimentary rock. I found this rock when I was visiting my daughter down south over Thanksgiving break and happened to see this interesting rock on a construction job site near her house. It was very eye catching as I saw the many different clasts formed into one solid rock. I only realized then it was some type of sedimentary rock which later accurately discovered it to be conglomerate. Finally the last rock I collected was up near Millerton Lake, familiar ground to where my children take their boat. I had a prediction that this type of rock was siltstone because of its smooth appearance with some indentations. After careful observation and research back at the house I concluded it was indeed siltstone.

Reference Page

http://geology.com/rocks/igneous-rocks.shtml http://geology.com/rocks/sedimentary-rocks.shtml http://geology.com/rocks/metamorphic-rocks.shtml http://www.wikipedia.org/

This was a tough, challenging yet exciting experience that I enjoyed very much. I hope after all the research and knowledge obtained throughout this class I was able to determine what rocks were correct.