On our second day, we stopped at an amazing outcrop where we could see multiple dikes, which we learned were created when molten rock intrudes surrounding rock and then solidifies. Here, we could see that the intruding rock had a much finer grain size than the host rock and contained more biotite, a dark colored mineral that forms platy crystals.
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| Emily standing by one of the dikes in the area! |
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| Mike notified the rest of us that there were huge dikes overhead as well. |
The dikes intrude the rock at certain angles and it's useful to record as much information as we can about their orientations. At this outcrop, we were able to practice taking a lot of strike and dip measurements with our Brunton compasses. Strike refers to the line at which the dike intersects with a horizontal plane, and dip is the angle from horizontal along which the dike intrudes. Using the right hand rule with your fingers pointing downhill along the dike, your thumb will point in the direction of the strike and your fingers align with the dip.
The outcrop area was massive--we scurried around taking measurements and learning about rock compositions in the area from Mike. A hand lens is extremely useful in studying the minerals that compose a rock because you can see the crystals a bit more clearly than you could with your eye alone, and Mike likes to remind us that we should have our noses to the rock if we want to use our hand lenses effectively.
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| An overview of the outcrop area with Mike, Emily, and Yuem |
Judy Pu
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