Quartermile in Edinburgh is a modern mixed‑use district built on the historic site of the former Royal Infirmary of Edinburgh, whose nineteenth‑century hospital buildings once dominated the area. The redevelopment, which began in 2004, transformed the 7–8‑hectare site into a blend of restored Victorian structures and contemporary architecture, creating homes, offices, and public spaces while preserving nine listed buildings. Its name reflects its location roughly a quarter mile from both Edinburgh Castle and the Royal Mile.
The tall buildings here may make it difficult to get a GPS fix. This EarthCache will take you to a concrete wall with a stone top, on the opposite side of the road to 14 Simpson Loan.
Why are we here?
We are here to study how xenoliths form in igneous rocks.
Igneous rocks form when molten rock originating from deep within the earth’s crust cools (either below the surface as an intrusion e.g. granite, or above the surface as an extrusion e.g. basalt lava). The resulting igneous rock is composed of interlocking crystals, the size of which depends on the time taken for the molten rock to cool. If the molten rock cooled rapidly, the crystals are small if it cooled slowly, the crystals will be large. A common building stone of the latter type is granite – due to the large crystal size in granite it is a very aesthetically pleasing rock, and is found in many forms, on buildings, being used for ornamental pillars and fountains etc.
Granite is a crystalline coarse rock, this means it is formed of crystals, and being coarse you can see these crystals. It is formed of three main minerals, which are :
- Quartz. This is a clear or greyish mineral, and is the most common mineral found on the surface of the earth.
- Mica. This is a black or silvery mineral, which look like flakes.
- Feldspar. This comes in a range of colours. Pink or white feldspar is known as orthoclase, whilst grey is known as plagioclase.
A xenolith is an inclusion in the magma which formed the granite and quite often it is part of the existing country rock into which the magma was forced. Once the magma cools, the xenolith appears to be a foreign rock fragment enveloped in the larger rock surface.
There is a good example in the stone marked below
How to log the cache:
Send me a message or an email with the answers to the following questions. There is no need to wait for a response before logging your find.
1) Describe the largest xenolith you can see - what size is it, what colour is it?
2) Describe how it looks different to the surrounding rock .
3) Why do you think the xenolith is there? Use the information above to help with your answer.
4) Take a photo of yourself at GZ, or an identifying item, being careful not to reveal any of the answers to the questions.