This EarthCache takes you to Swinegate in Leeds, where it meets the North Eastern Railway Viaduct. You need to look for a blue plaque, once you are here, then you can start to look at some geology.
North-Eastern Railway Viaduct.
This 1500 yard viaduct, including the New Station (now known as City Station was built over the river and canal. It was erected 1866-69.
The blocks which make up the viaduct are sandstone, which is a sedimentary rock, though there are plenty of EarthCaches which talk about sandstone and sedimentation, we are here to learn about, and see Liesegangen rings or Liesegang bands.
Liesegangen rings are to search bands that typically cut across the bedding in sedimentary rocks. You will notice that there are different beds in the sandstone blocks, these were laid down during sedimentation.
Liesegang rings are diagenetic structures. to seaDiagenesis means the change of a sedimentary rock, after initial deposition into a different form. It can take place due to a chemical, biological and physical change due to reasons such as temperature, pressures, and saturation with groundwater. They are formed due to authigenesis, which occures when a mineral deposit is produced where it is found. In the case of sedimentary rocks, authigenesis is due to precipitation or recrystallizarion of a mineral, commonly in the case of Liesgang lines, the mineral is iron.
Liesegang supersaturation-nucleation-depletion cycle
This is a long name isn't it? So lets simplify it, the rock is porous, which means that water and other liquids can pass through it. Minerals such as iron are carried in this water, though at times, parts of the rock got supersaturated. Imagine a sponge which is filled with water - it is supersatuarted. Then the minerals start to move by diffusion to other parts of the rock, so to produce a balance in the amount of the mineral. Though at times, localisation of minerals due to precipitation occurs, and crystal seeds form, these crystal seeds form bands, which in the case of Lieegang bands are known as rings. At times next to the rings you can get depletion of mineral in the adjacent areas, this may be apparent in differnce in colour or different chemical makeup when further analysed, which is beyond the realm of this EarthCache.
So lets look at the rocks here and the Liesegang rings. There are three areas to look at and then answer questions.
(1) STAND BELOW THE BLUE PLAQUE. Look directly above it. You can see a number of Liesegang rings. Please tell me, how many are there, and please describe the shape of the bottom one.
(2). GO TO THE CORNER WHICH IS NEAREST THE ROAD. Count up 4 blocks from the pavement. Please tell me how wide the Liesegang ring is here. There is evidence of mineral depletion occuring here, please describe the colour of the rock inside the ring compared to that outside of the ring.
(3) PLEASE GO TO THE OTHER CORNER. COUNT UP FIVE BLOCKS FROM THE PAVEMENT. Please tell me, is the ring, regular in shape, or irregular in shape. On the aspect of the block around the corner, please descrive the shape of the ring. How wide is line that forms the ring, and what colour is it? Is it flush with the rest of the rock, or does it stand out?
This being an EarthCache, in order to log it, I ask that you complete the above tasks. Please send the answers to me, and do not include them in your log. You can send them to me by using the message facility or email, both of which can be found by looking at my profile.