Review for Lab Exam 2 (week of October 20, 2014)
This exam will begin at the beginning of lab and will include questions from the Igneous and Sedimentary rock labs.
The lab will be open for review during tutor times, and some additional times so that you can review the rocks and minerals.
Maps and topography:
- Be able to use latitude and longitude (don’t forget to indicate N, S, E, W as needed).
- Use the bar scale and fractional scale on a map, and be able to determine distances from a map.
- Be able to determine a verbal scale by using the fractional scale and vice versa (see Part I of the topographic maps lab).
- Determine the contour interval (even if it is not indicated on the map).
- Know the difference between elevation and height, and be able to determine elevation, and slope (be careful not to confuse these terms).
- Be able to determine the direction a river is flowing based on topographic contours.
- Be able to determine the slope between two points on a topographic map. See practice homework problem.
Igneous Rocks:
1) Given an igneous rock sample*, you should be able to answer the following:
- Is it intrusive or extrusive?
- Describe the cooling history of the rock (did it cool slowly, quickly, or both?)
- What is its composition? (felsic, intermediate, mafic)
- You must be able to identify 1 or more of the coarse grained minerals in the rock
- What texture best describes the rock? (coarse, fine, porphyritic, pegmatitic, vesicular, glassy)
*Note: You should be able to answer these questions for any igneous rock we give you, even if you’ve never seen that particular rock sample before. The samples for this portion of the exam will not necessarily be exactly the same as the ones you saw in lab.
| |
Felsic |
Intermediate |
Mafic |
| Extra coarse grained |
granite pegmatite |
-- |
-- |
| Coarse grained |
granite |
diorite |
gabbro |
| Porphyritic |
porphyritic rhyolite |
porphyritic andesite |
-- |
| Fine grained |
rhyolite |
andesite |
basalt |
| If a rock is vesicular, you must include “vesicular” in the name of the rock (e.g. vesicular basalt) |
| Obsidian does not have any minerals (it is made of volcanic glass). As a consequence it does not fit into this chart. Pumice also is mostly glass and is also difficult to place in this chart. You must be able to identify obsidian and pumice, but you will not have to answer questions about their composition (felsic, intermediate, mafic). |
- You should also be able to identify the igneous rocks. The key to identifying igneous rocks is to know the rock chart (above). That way, if we give you a coarse grained, felsic rock, you will know that it’s a granite, even if you’ve never seen the rock before. You will have to ID igneous rocks that look different than the ones in lab, so do not just try to memorize what the rocks look like!
Sedimentary Rocks:
- Given a sedimentary rock sample**, you should be able to answer the following:
- Is the rock clastic, biochemical or chemical?
- You must be able to identify the dominant mineral(s) in each of the following rocks:
- quartz sandstone
- arkose sandstone
- all limestones
- rock gypsum
- chert
- For clastic rocks only, you should be able to relate the grain size of the rock to the energy of the environment in which it was deposited (low, moderate, or high energy environment).
**Note: You should be able to answer these questions for any sedimentary rock we give you, even if you’ve never seen the rock before. The samples for this portion of the exam will not necessarily be exactly the same as the ones you examined in lab.
You should also be able to identify the sedimentary rocks. The key to identifying sedimentary rocks is to know how to classify them (see below). Do not just try to memorize what they look like!
Clastic Sedimentary Rocks: classified 1st by size, 2nd by mineral content or roundness (when applicable)
- silt/clay sized (fine grained), tends to break into layers = shale
- sand sized = quartz sandstone or arkose sandstone, depending on the mineral content
- gravel sized = conglomerate or breccia, depending on whether the grains are mostly rounded or angular
Biochemical and Chemical Rocks: classified by composition, typically composed of just one mineral. Identify the rock by identifying which mineral it’s made of, or by recognizing special features such as fossils or ooids.
Chemical Rocks:
- rock gypsum: (gypsum) soft, can be scratched easily with fingernail
- chert: (quartz) made of microcrystalline quartz, therefore it is very smooth, has conchoidal fracture and is harder than glass
- oolitic limestone: (calcite) can be recognized by the presence of “ooids” which are small spherical grains of calcite.
- dolostone: made of the mineral dolomite (CaMg(CO3)2), which is similar to calcite, but will react to acid only when powdered. This rock should be softer than glass (unlike chert). Some of our samples in lab may scratch glass due to quartz impurities, but you can identify this rock by the fact that it reacts to acid when you powder it.
Biochemical Rocks:
- fossiliferous limestone: (calcite) can be recognized by the presence of whole and/or broken fossils
- coal: black, carbon-rich, low density