The Sentinel
Capital Boulevard (108 Street between 99 Ave and 104 Ave) underwent a redevelopment and was completed in 2014.
In 2017 for Canada150, 5 sculptures were installed along this boulevard, one of which is The Sentinel. Created by artist Sandra Bromley, it features rock layers from all 13 provinces and territories of Canada.
The Layers
This EarthCache is meant to bring you to this site to witness The Sentinel and learn about the different types of rocks.
The sculpture is smooth on one side an rough on the other. Touching these different surfaces can aid in your identification.
Granite
Granite is an intrusive igneous rock meaning that the rock was formed by cooling magma slowly inside the Earth. By cooling so slowly, large crystals form within its structure. Granite is a very strong rock and is a favorite in construction and decoration. Granite must contain at least 20% quartz within a rock to make it granite.
Granite is a varying mix of minerals and rocks, primarily quartz, mica, potassium feldspar, amphiboles, and trace other minerals. Granite typically contains 20-60% quartz, 10-65% feldspar, and 5-15% micas. The minerals that make up granite give it the unique colors we see in different types of granite.
Granite comes in a range of colors including a mix of white, pink, and black.
- Black generally come from an iron rich volcanic rock called Gabbro
- White comes from Quartz
- Pink comes from Potassium Feldspar
Quebec - Cambrian Black Granite
Ontario - Muskoka Granite
Saskatchewan - Saskatoon Granite
Sandstone
This is a clastic sedimentary rock formed from sand cemented together by minerals under pressure.
What makes sandstone unique is the size of the grains and the minerals in the particles determine the color. White sandstone contains a great deal of quartz, while back sandstone is high in iron, and red sandstone high in iron oxide.
The range of clastic sedimentary rocks is in this order from small particles to large particles:
- Siltsone/mudstone (particle size almost imperceptible to the naked eye)
- Sandstone (sand-sized particles)
- Conglomerate (cobbles and larger rocks combined with sand- and siltstones)
Prince Edward Island - Red Sandstone - The redness comes from the iron oxide (rust) contained within the sand.
Nova Scotia - Wallace Sandstone
Minerals
Minerals form the raw building blocks of rocks and can be pure elements on the periodic table or a mix of several elements. All three rock types (igneous, sedimentary, and metamorphic) contain minerals.
Newfoundland - Mariposite - This rock is a type of Mica and is tinged with small amounts of Chromium. It gets its name from Mariposa, California but is also from Canada. Mica is a mineral. The Chromium contributes towards the green colour.
Northwest Territories - Pyrrhotite - This is a mineral group which has varying iron contents and therefore can have varying levels or magnetism. Since it has a varying composition it can have two types of shapes: monoclinic and hexagonal.
Nunavut - Serpentine - This mineral is a part of a group, one of which is asbestos (don't worry it's not in this sculpture!). It is highly prized for sculpting by the Inuit people and is a cheaper alternative to Jade.
British Columbia - Nephrite - This mineral is one of the two varieties of Jade. It's sister Jadeite has the same physical properties and appearance; the only difference is that Jadeite comes in more varieties than green.
Limestone
Limestone is another type of seimentary rock called biochemical meaning that the rock originated from the remains of animals or plants. Coal is also considered a biochemical rock. Limestone is formed from the compressed skeletons of former animals. If the limestone is subjected to heat and pressure, marble, a much stronger (metamorphic) rock is formed.
Manitoba - Tyndall Stone - This rock is a variety of limestone (which itself is formed from the skeletons of ancient creatures which swam in an ancient sea 450 million years ago). This rock is used in many buildings in Edmonton and quite often you will see fossils in the rock.
New Brunswick - Brunswick Limestone - This rock is a carbonate sedimentary rock that is often composed of the skeletal fragments of marine organisms such as coral, foraminifera, and molluscs.
Other Rocks/Minerals
Yukon Territories - Rhyolite - This rock is an extrusive, felsic rock meaning that the rock cooled quickly on the Earth's surface (resulting in small crystals) but also light in colour due to a high silica content. The high silica content makes for a very thick, slow moving lava. Unlike granite, this rock has very small crystals that may be inperceptible to the naked eye.
Alberta - Rundle Rock - This rock is a sedimentary stone made up of either bits of shells or gypsum salt and calcium carbonate crystals that sank to the ocean floor 225 million years ago. The sand was compressed to form the rock over 20 -30 million years. It is fine-grained quartzitic siltstone or sandstone.
To Log This EarthCache
In order to log this EarthCache as "found" you must visit the site and answer the questions below:
1.) How many fossils are in the "Tyndall Stone" layer? Can you surmise what the fossil is of?
2.) What is the grain size of the sandstone? Do the two types of sandstone have similar grain sizes?
3.) The slower the cooling, the larger the crystals. Do you think this granite cooled inside the Earth?
4.) How many rough sides an how many polished sides are there?
Message me through the geocaching.com messenger with you answers with your log. Logs without accompanying answers will be deleted.
Thanks for visiting!
References
https://geology.com/rocks/mariposite.shtml
https://granitplus.com/en/Produits/cambrian-black/
https://www.minerals.net/mineral/pyrrhotite.aspx
https://www.minerals.net/mineral/serpentine.aspx
http://www.whaton.uwaterloo.ca/waton/s9911.html
https://www.rmoutlook.com/article/At-Kamenka-Quarry-every-stone-has-a-story-20160113
https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/rhyolite.html
https://www.forbes.com/sites/trevornace/2016/06/05/granite-colors-white-black-countertops/#4b2c02987b98