**Note the attributes**
In addition to the required photo (Q1), there are 3 questions to be answered (Q2 a&b, Q3 a&b). Please read the logging requirements carefully to avoid disappointment. All logging requirements must be met to log an EC as "found".
You will be looking at the outer walls and comparing the stone found there to the coloured and polished stone at WP1, which can be found immediately as you enter the Union Mall. You DO NOT need to enter any part of the National Rail station to complete this EC.
I will read and respond to all submissions. Please recall that to claim a find for an EC, the logging requirements must be met and that answers need to be sent, first.
Responses to submit - if submitting responses for a partner, be sure to include their geocaching name with your response. EACH PERSON, however, must submit their own photo demonstrating they were on site (see Q1 below).
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1. Required photo for all cachers - take a photo of you/ your GPS / your caching name in front of Aberdeen Station. See the spoiler photo so that you know exactly what photo is expected.
2. Thinking questions - This task will have you looking at the outer granite walls of Aberdeen station and compare your observations with the polished granite found immediately inside the Union Mall. We are specifically looking at granite formation.
a) Posted coordinates - look at the outside wall of Aberdeen Station. Describe the crystal structure, mineral size, colour and any other physical properties that you observed.
b) WP 1 - Look at the multi-colour granite floor. Your task is to identify 1 obvious, naturally-created anomaly in the rock (hint: they will look completely different from the surrounding rock). It is easier to find the xenolith if you look at the coloured granite rather than the darker granite. Describe and measure your chosen xenolith. If you find something that looks like the granite but is a slightly different shade, that's not a xenolith. Send me a photo of your xenolith to ensure that you've identified the correct geological item. Do not post this with your log. IM works best for this task.
3. Application questions -
a) Based on your observations at GZ and WP1, how long did it take for this granite to cool (during formation), and what does its crystal size tell us about its formation? Explain your reasoning.
b) Which rock is older - the xenolith or the granite? Explain your reasoning.
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Granite in Aberdeen
Granite is integral to the identity of the "silver city" of Aberdeen. "Many of the city's most well-known buildings are built from rocks that come from large quarries, the most famous was the Rubislaw Quarry in Aberdeen's west end. Aberdeen became the granite capital of the world by the end of the 19th century with the advances in technology that aided in the transport and carving of the rock, with more than 50 percent of the buildings coming from the Rubislaw Quarry. Portsmouth, Southampton, Waterloo Bridge in London and House of Parliament in London all used the granite from Rubislaw Quarry. The granite industry would decline after the mid-20th century as building started to use glass, steel and concrete for construction." (Future Museum).
Aberdeen station, like much of the "Granite City" is primarily constructed from local silver-grey granite. This durable stone was sourced from nearby quarries, most notably the famous Rubislaw Quarry. The granite is known for its sparkling, durable nature, which characterizes the station's architecture.
Key Facts about the Stone:
- Material: Granite (specifically Aberdeen Granite Pluton).
- Appearance: Silver-grey, sometimes with red or pink tones.
- Source: Rubislaw Quarry.
- Geological Age: Formed during the Ordovician Period (approx. 475 million years ago).
Granite Formation
Granite is an intrusive igneous (or plutonic) rock, formed from slowly cooled magma deep underground, resulting in large, visible crystals of quartz and feldspar. Examples include granite, gabro, diorite and pegmatite. On the other hand, there are also extrusive igneous rocks that form from rapidly cooled magma that "explodes" through volcanic activity. Examples of this type of rock include tuff, basalt, pumice and obsidian.
Let's take a closer look at the granite floor and the xenoliths within
A xenolith is a piece of rock trapped in another type of rock. Xenocrysts are a type of xenolith—one type of rock trapped in another type of rock. Xenoliths are usually visible. They have a different colour and density than the surrounding igneous rock. Xenoliths can be as small as a grain of sand or as large as a football, and as long as several meters.
Most of the time, a xenolith is a rock embedded in magma while the magma was cooling. Magma is the molten rock beneath the Earth's crust that emerges as lava during a volcanic eruption. The rock that forms from cooled magma is called igneous rock. Xenoliths are different types of rock embedded in igneous rock.
Xenoliths are torn from deep cracks, or pipes, in the Earth's surface. Magma rises to the Earth's surface through these pipes between the Earth's crust and mantle. As the molten material rises, it tears off bits and pieces of the magma pipe in which it is travelling. These bits and pieces, trapped in the magma but not melting into it, become xenoliths. Crystals that are torn from the sides of magma pipes are called xenocrysts.
Sources:
- my own knowledge (geology degree)
- completion of hundreds of ECs
- National Geographic, Xenoliths; Future Museum, The Granite City
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SideTracked Caches and the History of the Station:
The station currently standing was built and opened in 1867, although the station today has been significantly redeveloped from the original. The station and the new Denburn Valley Line enabled the main line from the south and the commuter line from Deeside to connect with the line from the north. The lines from the south had previously terminated at the adjacent Aberdeen Guild Street. Even this had not been Aberdeen's first railway station, that distinction belonging to a previous terminus a short way south at Ferryhill.
Prior to the construction of the Joint Station, lines from the north had terminated at Aberdeen Waterloo, a short but inconvenient distance along the edge of the harbour. This too became a goods station after the construction of the Joint Station.
(Wikipedia)