This is an Earth Cache! No physical hide is here, but rather a lesson on geology instead! Using the rock at this location and the following lesson please answer the questions below!
Before you is a boulder moved here during the construction of the park. Surrounded by bricks and walking paths, it has sat here facing the elements and countless kids climbing on it over the years! But what kind of rock? How have the years of Minnesota weather and kids affected this boulder?
Sedimentary vs. Metamorphic vs. Igneous
Sedimentary rocks form from the deposit of fine sediment millions of years ago. Over time, the pressure of the earth press the sands together into a hard stone. These rocks often look like sand and can have layers on their sides that look like pages of a closed book.
Metamorphic rocks started out as either sedimentary or igneous rocks, and went under intense heat and pressure, changing their appearance and makeup. These types of rocks can show layers of crystals, slabs of rock that is easily broken off in sheets, or ribbony layers like marble stones.
Igneous rocks are the result of volcanic activity! Sometimes magma cools slowly under the earth's surface which acts like a blanket resulting in lumpy looking rocks with big crystals in them. Other times the lava cools quickly on the surface of the earth resulting in shiny or fine grained rocks.
What kind of rock is this?
The rock we are looking at is known as Basalt. Basalt is an igneous rock made up of minerals such as feldspar, augite, hyperthene, and olivine. It is formed when magma that is rich in iron and magnesium but poor in silica (quartz) breaks through the earth's crust and turns into lava. When exposed to the open air, it cools quickly forming small crystals. This results in a dark grey to black rock that, when exposed to weather, may turn yellow or brown on the surface. Crystals may or may not be seen by the naked eye.
Weathering and Erosion
Rocks left outside go through a lot! The changing of the seasons, rain, plants, and even people can slowly chip away at a rock making it smaller over time. Here are some examples of weathering and erosion:
Physical
>Frost Wedging is the result of water seeping into cracks of the rock and freezing. As the water expands, it wedges the rock apart.
>Thermal Stress happens when the rock expands and contracts as it warms up/cools down outside
Chemical
>Dissolution happens when acids in water dissolves the rock
>Oxidation is when iron bearing minerals react to the outside elements and rusts, weakening the rock
>Hydrolysis and Carbonation is when water changes the makeup of the rock
Biological
>Plant roots or the presence of lichen can break down rocks over time by splitting the rock at cracks
>Human/Animals can weather rocks by walking on them, climbing on them, burrowing underneath or in them. Over time the friction of interacting with the rock can wear it down.
Water Erosion generally happens when impacts of raindrops remove microscopic amounts of rock, or when flowing water on the rock's surface wears it away. Generally sedimentary rocks are more susceptible to this than harder rocks sich as igneous rocks.
Wind Erosion is caused by the wind moving across the face of a rock. The wind can act like a sand-blaster by carrying fine particles and impacting the rock, wearing it down. The wind can also carry particles off the rock slowly breaking it down over time.
The Mythical Weather Rock
Did you know sometimes rocks can tell the weather? This one can.
Here is the weather forcast based on the appearance of the rock:
Rock is Wet - - - - - Raining
Rock is Dry - - - - - Not Raining
Shadow on the Ground - - - - - Sunny
White on Top - - - - - Snowing
Can't See Rock - - - - - Foggy
Rock Bouncing Up and Down - - - - - Earthquake
Rock is Gone - - - - - Tornado
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Please answer the following questions by either emailing them to me or by contacting me through the messenger system. Please do not post answers in your log
1) What colors do you see in the rock? Any ribbons of color through the rock?
2) Describe the rock's texture and appearance. Are there flat faces? Sharp or round edges?
3) What forms of weathering and erosion do you think are present here?
Optional Question just for fun you can include in your log!
A) Based on the Weather Rock chart above, what is today's forcast?