This EarthCache is based inside the Arndale Centre in the centre of Manchester, a modern building with a colourful history.
The fabric of the building includes a number of decorative and geologically interesting rocks, formed millions of years ago,
As with any indoor environment, GPS tends not to work very well so please take note of waypoints / directions provided on this cache page to be sure you arrive at the correct location to complete the logging tasks.
Thank you to Team Microdot for his help with both making this EarthCache and helping get permission for it.
This EarthCache has been kindly given permission by the Arndale Centre.
Waypoint 1 is at the "Exchange Court". You will need to go to the bottom of the steps here. You will see a green rock on the floor here. This is the rock you need to look at.
Waypoint 2 is at the bridge over the "Exchange Court". Climb to the top of the stairs and take a left turn. From here, you will see the bridge. Here, there is another green rock on the floor. This is the rock you need to look at.
A migmatite is a rock that is a mixture of igneous rock and metamorphic rock. It is created when a metamorphic rock such as gneiss partially melts, and then that melt recrystallizes into an igneous rock, creating a mixture of the unmelted metamorphic part with the recrystallized igneous part. They can also be known as diatexite.
Typically, the rock contains alternating lighter layers (leucosomes, comprised of light-colored minerals such as quartz, feldspar, and muscovite) and darker layers (melanosomes, comprised of dark-colored minerals such as amphibole and biotite).
The heterogeneous (the diverse in character, in this case, the colour) nature of the rock results from partial melting (called anatexis) that occurs when a precursor rock (the original parent rock) is exposed to high pressures and temperatures.
The light-coloured layers originate from the partial melting and have igneous characteristics– that is, their appearance indicates that they have been crystallized from a melt.
The dark-coloured layers have experienced metamorphism, but they do not have igneous characteristics. The distinctive light-and-dark banding ) as well as the folding commonly found in this rock results from the partial melting as well as from high-grade metamorphism and deformation.
In the rock at GZ, you will know that it is banding that you see if you can see a lighter green and a darker green contrasting each other.
Rocks at GZ
There are 2 waypoints to this EC which both lead to 2 "different" rocks. These rocks are both the same but have been cut differently into a certain way to give them a certain appearance. These are both migmatites.
I am not going to give the name of the rocks however I will be thoroughly describing them and you will have to identify which rock appears where.
The rocks will be referred to as Rock 1 and Rock 2.
Rock 1 is a dark green rock with lighter green "bands" in it. These "bands" are a lighter green colour and appear to be in random sizes and directions throughout the rock.
Rock 2 is a dark green rock but the banding is less obvious. The banding has been cut parallel to with the fold axes so the banding appears to be straight and parallel. The light green doesn't appear to be as obvious here but it can be seen if you look carefully.
Please send me your answers via my Geocaching profile either by an email or through the messaging centre. Once you have sent your answers, you may log the cache.
1. Which rock features at which Waypoint?
2. In both rocks, give an estimated % for the amount of the light green banding you can see in rock.
3. At both Waypoints, the rock has been cut up into square sections and then been used on the floor. In Rock 2, are these squares of the rock similar? Please describe any similarities and differences that you see