Devil's Courthouse

Take a look at what we have in the parking lot! Not only can you see where we're going to hike to, but there's an interesting mineral here too...

At this point, you've gotten some basic practice at making geologic observations. Now you're going to look through these pictures before you are prompted. What stands out to you? It absolutely takes practice to be able to make the necessary observations when in the field, but it's a really good skill to start learning. So, take a look at these photos. A lot of them have captions to give you a little help. Write down in your field book what stands out to you, then you can read the following questions and see if you were able to make all of the observations in our discussion.

Reminder: The starting point of the 360° photos are out of our control, so in addition to enjoying the awesome views, please remember to rotate to look down at the rocks!

Parking lot:

Outcrop:

Once you've finished exploring and making your initial observations, see if you can answer these questions...

1. What do you think that black mineral in the parking lot could be? What do you notice about it's shape and where it's located in the rock?

2. What do you notice about the degree and type of deformation that took place here (particularly in the photos from the trail)?

3. What grade of metamorphism do you think is on top of the outcrop? Slate? Phyllite? Schist? Gneiss? Migmatite? (Check your field guide for help!)

4. What erosional feature do you see?

If you didn't notice these things, you are encouraged to scroll back up and look again! (It's okay if you missed some! This is how you practice and train your mind to think like a geologist).

Let’s talk about some of what we see here.

First, in the parking lot, those black minerals are very large magnetite crystals. While we don't usually see magnetite crystals this large, well-formed, or in bands like this, they are very common as tiny crystals in most rocks. You may not have come to the conclusion that they were magnetite, as you weren't given a lot of information. What are some observations that could have helped you figure out it was magnetite?

For starters, it was highly magnetic. The compass needle immediately turned when next to the rock. That little piece also had a high specific gravity. Remember how we talked about the density of heavy minerals in Stop 4?

From looking at the outcrop, you can see that it formed in bands. There are a few different explanations, but as a general rule of thumb (especially since you can see other indicators of metamorphism in the area), metamorphic minerals tend to grow in bands.

Additionally, looking at the outcrop, you can see that the black minerals stick out of the outcrop, telling us that they are less erodible (harder) than the surrounding minerals.

As you look through the photos from the trail, you see ductile deformation in differing amounts. Ductile deformation happens when rocks behave less like a solid, and more like Play-Doh. Of course this kind of deformation takes place over millions of years, meaning that the rock would appear solid when observed over our time frame. Think of this like massive forces that are able to stretch and squish entire mountains as if they were soft!

In the simplest sense, think about ductile and brittle deformation like this: brittle deformation is what results in faults, while ductile deformation results in folds. Brittle deformation happens when something is strained and breaks, like a twig snapping in half. Ductile deformation happens when something bends in response to strain, rather than breaking.

When we get to the top of the mountain, in addition to the great panoramic views, the rocks beneath us are also pretty interesting.

If you look at them, you can start to pick out some compositional banding. If you try to follow this for very long, you see it becomes wavy and more difficult to follow. This tells us that this rock was likely getting hot enough to start becoming a migmatite, which has properties of both metamorphic and igneous rocks. What must happen to form a migmatite? Before you get a migmatite, a rock will first become a gneiss with mafic and felsic compositional banding. Back at Stop one, we talked about how mafic minerals are higher up on Bowen's Reaction Series than felsic minerals.