Geology 101: Extra Credit Rock Collection and Analysis
For extra credit, you can collect up to 4 rocks from natural, in-place settings, not artificially moved to
where you found them, preferably from outcrops of bedrock.
The rocks must be of the following types: plutonic igneous, volcanic igneous, clastic sedimentary, and
regional metamorphic.
For each rock:

Number the rocks 1-4, where 1=a plutonic igneous rock, 2=a volcanic igneous rock, 3=a clastic
sedimentary rock, 4=a regional metamorphic rock. The rocks must be small enough to fit in a
sandwich-size ziplock bag, either all together or individually. Be sure your name and the sample
number is on each rock or else in or on its bag.
Write up an analysis of each rock as follows:
1. State exactly and precisely where the rock was collected, and state whether it was collected
from an outcrop of bedrock or from loose sediment. Describe the outcrop or loose sediment.
2. State whether the rock is plutonic igneous, volcanic igneous, clastic sedimentary, or regional
metamorphic.
3. State which minerals are in the rock. For each mineral in the rock, state which physical
properties of the mineral you were able to use to identify it.
4. Describe the texture of the rock, appropriately for its rock type. For example, igneous rocks have
texture terms such as highly porous, or porphyritic, to give two different examples. Clastic
sedimentary rock have textures described in terms of grain size, grain sorting, and grain
rounding, which refers specifically and only to those grains in your particular rock. Metamorphic
rocks textures are described in terms of type of foliation and grain size.
5. Describe how that rock formed in terms of geological processes. The rock cycle briefly outlines
the basics of these geological processes, but you may be able to be more specific in some cases,
such as with the clastic sedimentary rock, for which you can hypothesize its erosional source and
depositional environment based on its minerals and texture.
a. If a rock was collected from loose sediment rather than an outcropping of bedrock,
hypothesize the erosion, transport, and deposition process that likely brought it there.
The collected rocks and the machine-printed write-up together are due by Friday, March 19.
Extra credit of up to 5 points per rock is possible.