This EarthCache takes you to Kettlewell Church, more specifically the side door. The church is constructed from sandstone, which is a sedimentary rock. We are here to look at a feature in the sandstone, which are called Liesegangen rings.
The below photograph shows where to look.
🤔What is sandstone?
Sandstone is a sedimentary rock, formed by sediment which has been laid down. In the case of sandstone, the sediment is sand and gravel.
➡️ How does it form?
The formation of sandstone involves two principal stages:
🔸️Initially a layer or layers of sand accumulate as the result of sedimentation, either from water (as in a stream, lake, or sea) or from air (as in a desert). Typically, sedimentation occurs by the sand settling out from suspension; i.e., ceasing to be rolled or bounced along the bottom of a body of water or ground surface (e.g., in a desert).
In the case of this location, the sandstones were deposited in a river delta environment.
🔸️Finally, once it has accumulated, the sand becomes sandstone when it is compacted by pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains.
The most common cementing materials are silica and calcium carbonate, which are often derived either from dissolution or from alteration of the sand after it was buried. Colours will usually be tan or yellow (from a blend of the clear quartz with the dark amber feldspar content of the sand). A predominant additional colourant is iron oxide, which imparts reddish tints ranging from pink to dark red, with additional manganese imparting a purplish hue.
🤔 We are here to learn about Liesegangen rings.
Liesegangen rings are bands that typically cut across the bedding in sedimentary sandstone. Bedding refers to the layers of sedimentary rock, with each individual layers known as a bed.
Liesegangen rings are diagenetic structures. Diagenesis 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 recrystallization of a mineral, commonly in the case of Liesgangen 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.
This being an EarthCache, in order to log it, I ask that you answer some questions. Please send them 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.
1. Please describe the Liesegangen rings here, in terms of how many, and their colour.
2. What process causes them to form?
3. Is there any mineral depletion evident? If so, please explain the rationale for your answer.