EDUCATIONAL LOGGING REQUIREMENTS
In order to substantiate your visit and comply with the educational requirement for Earth Caches you have to submit your answers to the following questions to the cache developers via their profile:
For purposes of logging this cache you must answer the following five questions.
1) Identify the type of rock using the table below.
2) Describe the three materials making up the rock. If possible give their names though this is not essential.
3) Look at a number of the crystals in the stone. Measure their length, average their size and then state whether the rock is coarse, medium, or fine grained using the following scale: Coarse crystals over 5mm in length, Medium crystals between 1-5 mm in length, or Fine crystal less than 1mm in length.
4)What is the shape of the trough. References to a type of food or a computer game will bring a smile.
5) Is this plutonic or volcanic rock?
|
The Prince of Wales Obelisk was brought to South Africa by the founder of the Eastern Province Herald, John Paterson to be placed on the grave of his partner, George Kemp. The Kemp family donated it to the city. The City decided to erect it in front of the city hall Market Square to commemorate the Prince of Wale’s marriage to Princess Alexandra. This was done on 22 May 1863. Four water troughs were added in 1877/8 and were filled with water during a “tap ceremony” when water was first piped to Port Elizabeth. The obelisk was removed in 1921 and stored until 1975 and now stands at Bay World. One of the water troughs was placed on the lawn at the Walmer Town Hall. The location of the other three troughs is unknown. You are now standing at the water trough.
While the history and the origin of this item is fascinating, this time we are interested in the very hard rock that the trough is made out of.
Igneous rock (derived from the Latin word ignis meaning fire) is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Over 700 types of igneous rocks have been described, most of them having formed beneath the surface of Earth's crust. Igneous rock is classified using the composition of the rock and the relative percentages of Quartz, Alkali feldspar, Plagioclase, Feldspathoid (the QAPF diagram).
This trough is made out of igneous rock and was formed when different types of rock melted and formed a new rock when the molten rock cooled and crystallised. It has a granular structure containing many grains. If you look closely you will see three different materials making up the stone.
The current theory of how such a rock is formed as follows. Below the surface of the earth lies molten rock magma. Floating on this sea of magma are plates of solid rock.They are the tectonic plates which are in constant movement . Where the plates meet one plate will slide on top of another plate forcing it down into the sea of magma. The downward pressure causes some of the molten magma to swell up in bubbles and melt some of the rock above.
The molten rock under great pressure from the solid plate above cools slowly to form crystals. Not all the original rock melts and fragments of it remain in the rock. This gives a clue to how this rock formed. The newly formed crystals of rock are forced up and expand as they are under less pressure. This two stage process forms the rock used in the making of this trough. There are other theories on how this rock is formed with consensus being that there are a number of different ways.
To claim this Earth Cache as a find please send me an email with the answers to the five questions, your caching name and your email address through our profile.
You may log your find once you have visited the site and determined the answers to the questions. Logs not supported by the necessary email will be deleted. Please do not reveal the answers in your log!
The information to answer the questions can be found by looking carefully at the stone and reading the description of the cache
Igneous rocks which are light in color are on the left and those which are dark in color are on the right. The top row of the chart contains the plutonic rocks and the second row contains the volcanic rock equivalents (in terms of composition). For example, a volcanic rock which is light in color is called a rhyolite. According to this classification method, a rhyolite contains approximately 5 % to 25 % quartz, 62 % to 74 % feldspar, and 10 % to 25 % ferromagnesian (iron and magnesian) minerals.
References
Wikipedia
National University of Colombia website for the diagram
Afrikaans Wikipedia
Spoiler
This is NOT the object you are looking for.
