As you wonder through the Dales, you will notice lots of limestone, sandstone, geological features and much more, but if you take a bit of time to go away from the main paths and tracks there is plenty to see. This EarthCache takes you to an amazing waterfall on the slopes of Dawson Close. Be careful, it is rough, uneven and rocky underfoot. The whole area is littered with fossils, but we are here to look at something else - a Nodule. The nodule is in the walls of the low cliff.
Sometimes, when looking at the landscape and geology there are large features, and there are small features, this EarthCache fits into the later category.
So what is a Nodule?
A nodule can be described as a small lump of a substance, that is differnt from the surrounding rock.It can be irregular in shape and may have a knobbly surface. What we are here to look at, is a nodule of Haematite.
Haematite is an iron oxide mineral, and nodules of this types often form in sedimentary rocks, due to precipitation into cavities by an iron rich solution. This solution can often form crystals such as pyrite or marcasite, with oxidisation of these crytals then forming haematite.
So what is Iron Pyrite?
It is an Iron Sulphide, and is found in all types of rock – (igneous, metamorphic and sedimentary) as well as in hydrothermal vents. Its formation can be in a variety of ways:
Igneous Rocks. In this situation it is formed from the minerals in magma, which seperated out, depending on the temperature as it cooled, with crystals being formed.
Granite. A type of igneous rock.
Metamorphic Rocks. These rocks are formed by heat and pressure, and in this situations, the pyrite could have been formed as the process of metamorphism takes place, or as a replacement mineral in the rock.
Marble. A type of metamorphic rock
Sedimentary Rocks. With this type of rock, pyrite is usually found as a replacement mineral, when iron and sulphur present in the sediments combine to replace the original chemical composition of organic matter.
Limestone. A type of sedimentary rock.
Sandstone. A type of sedimentary rock.
This is not meant to be a difficult EarthCache, the idea is to show you this element of geology, so you can learn from the experience, and hopefully if you spot another in the future, will know what it is. In order to show that that you have visited the EarthCache location and learnt from the experience, I ask that you answer the below questions. 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.
(1) How many haematite nodules are there?
(2) Please describe the nodule in terms of shape, its dimensions in cm, its colour, and appearance.
(3) How high up the low cliff is the haematite nodule?
(4) Please identify what type of rock the nodule is in.
(5) Using the information from question 4, please tell me, how the nodule was formed.