Things you will need to log this Earthcache:
- GPS
- At least a 12' tape measure (a smaller ruler can be used but will require more effort)
- Camera (optional)
The logging requirements for this Earthcache can be emailed to me, via my profile:
- Tell me the color of the host rock?
- Can you see crystal shapes in it?
- What is the size of the largest xenolith you can see?
- Tell me the colors of the most common xenoliths?
- How many different types of rock are the xenoliths?
- A photo can not be required, but is always appreciated.
Due to the number of Earthcache answer emails I receive, I will not reply unless there is an issue with your answers. If you wish to have contact with me, please send a separate email. Thanks.
Xenolith
The name comes from the Greek for "foreign rock".
Xenolith is a fragment of foreign rock within an igneous rock. Xenolith itself may be any type of rock but its host rock has to be igneous. Foreign rocks in other rock types are known as inclusions. Xenoliths will typically have a different color and density than the surrounding igneous rock.
Magma
Is the molten rock beneath the Earths crust that emerges as lava during a volcanic eruption or creates structures under ground. The rock that forms from cooled magma is called igneous rock.
Geological History
The large dark rock you see at the child waypoint is most likely not from Michigan. It could have come from the bed of Lake Superior or most likely from Canada. The bed rock below ground here are sedimentary rocks, such as sandstone (like the three rocks to the west) and limestone. These bedrocks can be found from this location to the northern shores of the upper peninsula's Lake Superior shores.
Over the past few million years glaciers have moved south from Canada to the Ohio River several times. Each time they moved south, they broke off pieces of the bed rock. That's how this rock arrived here, but that's not the lesson here. As a side note, this rock was unearthed when the power plant across the road was built.
This lesson is about Xenoliths
As the magma works it way towards the surface, it is forcing it's way through the existing bed rock. Some of the bed rock is melted into the magma and some of it is broken off (these are the Xenoliths) and flows with the magma. Sort of like when a ice covered river starts to break up. The river becomes a mix of flowing water and pieces of ice.
What looks to be very unique with this rock is the number of Xenoliths that can be found with the it. I am researching on what is a common number of Xenoliths that are found in any one rock. And what is the most. I will be updating this info as soon as I get an answer.
Smaller pieces of Xenoliths will be melted into the magma. The larger pieces will partially melt and will look like a water worn rock. Some pieces will retain there broken surfaces. You will see different examples of Xenoliths in how much they have melted and of what type of rock it is. All Xenoliths I saw in this example are igneous types.
Xenoliths starting to form.
Xenoliths have moved closer to the surface and have started to melt.
Xenoliths have moved even closer to the surface and have continued to melt.
References used:
- http://nationalgeographic.org/encyclopedia/xenolith
- http://www.data.com/Xenolith/Xenolith/www.sandatlas.orgxenolith/Xenolith.htm
- https://en.wikipedia.org/wiki/Xenolith