Earthcache Overview
There is no container to find on site, but three slab rocks with the words “Lest We Forget” etched on them. They are a great example of telling a story of gneiss formation in one place. You can visit anytime, although if there is a lot of snow on the ground, some features might not be visible. Only a camera or cell phone is necessary. All information is included in the listing.
Logging Tasks
No science degree answers expected. All attempts at answers are welcome. You may log a find when you submit them and will be contacted if there is an issue.
Include in your log the photos described in tasks 1 and 2. Send me a message with the answers to tasks 3, 4 and 5.
1. Include with your log a photo of you, or a personal object, with at least two the "many eyes" or Augen. Your face does not need to be in the photo.
2. Include with your log a photo of you, or a personal object, of your favourite feature of these colourful stones. Bonus marks if you add the name of it. Your face does not need to be in the photo.
3. In your own words, what causes the folding and bending in gneiss?
4. Looking at the three rocks, do they all contain boudin, folds, augen and bands or are some of them missing?
5. The darker zigzag line at the bottom un-engraved side of the largest stone shows more movement than the thicker layers around it. Why do you think this might be?
Geology Lesson
Many of us put countless hours into getting the complement of “Nice Abs”.
Our earth has put 2 Billion Years into creating these “Gneiss Slabs”.
These stones might have even been though the process twice in that time.
These 3 rocks are called gneiss, which is metamorphic granite that is formed with heat and pressure deep within the earth’s crust. It is usually formed through tectonic plate shifts which cause this heat and pressure. When they are all underground together they are free flowing and resemble a lava lamp. They separate due to mineral types, specific gravity, particle sizes and move around slowly when at the earth's surface.
Gneiss is primarily made up of quartz, feldspar (usually orthoclase), and mica minerals. The pinkish specks and layers are the feldspar, the darker mineral areas are mostly biotite and hornblende, and the sparkly or grey coloured regions are quartz.
When the intrusive igneous (having solidified from lava or magma or volcanic) granite undergoes this metamorphisms through heat and pressure, it results in the beautiful banding patterns shown within this gneiss.
The gneiss forms in layers, and they get squished and squeezed. Some end results are straighter bands, augens, boudins, folds and zig zag patterns. All are present in these three stones.
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Banded Texture – characterized by alternating darker and lighter coloured bands in the cross section.
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Augen Gneiss – Augen is from the German name for “eyes”. These are like “bubbles” preserved in time as the rock cooled and formed after the layers. Augen are large, oval shaped crystals of feldspar.
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Boudinage is where a layer is stretched, and deformed, broken up into sausage shaped boudins. Boudin is the French word for sausage.
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Folding or twisting – Layers that are subjected to more stresses while cooling appear as folds or zig zag patterns. If there is no room to go laterally, the layer buckles.
If you visualize the largest stone from the un-engraved side, the flow came from the bottom left, the bigger layers forming first and then straight down the right side creating a pegmatite vein. A pegmatite vein also contains quartz, feldspar or mica but in big crystals.
There are two instances of post main formation cracking on this ungraved right side. Some appear as fine, straighter lines and other larger deeper cracks.
The smaller stones show iron staining on the top compared to the top surface of the main stone. This reflects an older fracture along a crack, while the larger stone is a newer break.
Looking at the largest stone from the engraved side, note the black stuff that has broken up a bit, and floated down. It would be high in iron content minerals.
Excellent large quartz are visible on the top left corner above the pegmatite vein. Pink feldspar is next to it. Still looking at it from the top you can see how the large, dark coloured amphibolite layer with more matic minerals such as magnesium and iron thins out and then thickens again. Amphibolite, another metamorphic rock, contains amphibole, especially hornblende and actinolite, plagioclase feldspar with little or no quartz.
We suspect that all three stones were part of the same formation. These stones are not native to the area, but came here from India.
Admin Notes
Roadside parking is available closeby and is waypointed. This should be wheelchair accessible at all times except in times of snow accumulation.
Sources
Peter Russell, Retired Curator of the Earth Sciences Museum, University of Waterloo
Tristan Mineault, Assistant Museum Curator, Earth Sciences Museum, University of Waterloo
Wikipedia
Geologyin.com
Jon at All Things Earthcache on youTube