It’s hard to believe when looking at the peaceful, rural scenery of the Eden Valley today, that hundreds of millions of years ago, this wet and windy area of Northern England was on, or close to, the Equator and that the hugely diverse rocks that make up this landscape were formed when the topography of the land and our climate was very different. More recently, geologically speaking, the area was covered by vast sheets of ice which carved out river valleys and high fells, exposing the rocks that shaped the landscape, enabling us to understand much more about the earth’s formation
Rickerby Park has its own stone circle with standing stones of rock hewn from the three main rock types which are all found in the catchment area of the River Eden, which rises on Mallerstang Common and flows into the Solway Firth at Bowness on Solway. The stone circle features Kirkstone slate, Penrith red sandstone, millstone grit, Shap granite and Shap Fell limestone. It was commissioned by the Eden Rivers Trust and was funded as part of a Heritage Lottery Fund grant
What are the rocks actually made of?
Essentially, they are made from grains of minerals that fit together. But, only a few minerals are rock forming and most rock is made from a combination of the commonest of these such as feldspars, quartz, mica, calcite, and amphiboles. But other minerals can also be present. Zircon is one example of an “accessory” mineral found in sandstone and granite. Most of the accessory grains are resistant to weathering and can indicate the maturity of the rock. Although Zircon means golden coloured, it can vary in colour from yellow to red, blue and green. Other accessory minerals include topaz, which can be found in granite such as that found in Cairngorm, garnets, often found in metamorphic rocks and tourmaline, found in sedimentary rock. These accessory minerals are often used in industrial processes because of their crystal properties but are also commonly displayed gem stones in jewellery, with zircon often used as a substitute for diamonds.
Sadly, although several of these accessory minerals can be found in the rocks making up this stone circle, they are only present in microscopic amounts that are invisible to the naked eye. But, that doesn’t make the stones any less interesting. The durability of the overall rock and the richness of some of the minerals present means that for thousands of years, man has exploited this abundant resource for all manner of uses, be that for building, industrial or engineering use or for decoration and displays of wealth.
Formation of sedimentary rocks
A river carries, or transports, pieces of broken rock as it flows along. When the river reaches a lake or the sea, its load of transported rocks are deposited on the bottom. The deposited rocks build up in layers, called sediments. This process is called sedimentation. Skeletons of animals and plant debris can also become trapped in the layers, revealing themselves millions of years later as fossils.
The weight of the sediments on top squashes the sediments at the bottom. This is called compaction. Water is squeezed out from between the pieces of rock and crystals of different salts form into a cement that binds the pieces of rock together.
These processes, which make take millions of years, eventually make sedimentary rocks such as sandstone
Formation of Igneous rocks
The inside of the Earth is hot enough to melt rocks. Molten (liquid) rock forms when rocks melt. The molten rock is called magma. When the magma cools and solidifies, a type of rock called igneous rock is formed. Igneous rocks contain randomly arranged interlocking crystals. The size of the crystals depends on how quickly the molten magma solidified. The more slowly the magma cools, the bigger the crystals in the resulting rock
If magma erupts from a volcano, it cools very quickly into rocks such as Obsidian and Basalt which are formed of smaller crystals. They are called extrusive igneous rocks because they form from eruptions of magma.
Magma cools more slowly when it’s underground, which is why Granite is composed of bigger crystals. Granite is an intrusive igneous rock because it was formed from magma underground. Granite always consists of the minerals quartz and feldspar, usually with a wide variety of other accessory minerals. The quartz and feldspar generally give granite a light colour, ranging from pinkish to white. That light background colour is punctuated by the darker accessory minerals giving classic granite a "salt-and-pepper" look. The most common accessory minerals are black mica biotite and the black amphibole, hornblende. Shap granite is very distinctive as it contains a lot of pink feldspar and several specific minerals including zircon, magnetite and titanite
Unlike sedimentary rocks, igneous rocks do not contain any fossils. This is because any fossils in the original rock will have melted when the magma formed.
Formation of Metamorphic rocks
Metamorphic rocks are formed from either sedimentary or igneous rocks that have been subjected to heat or pressure. One common cause can be as a result of earth movements that cause rocks to be deeply buried or squeezed. As a result, the rocks are put under great pressure which causes them to be heated. They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks. Metamorphic rocks are also formed when an existing rock is close enough to molten magma for the minerals to change composition but are not close enough to melt.
When a metamorphic rock is formed under pressure, its crystals become arranged in layers. Slate, which is formed from shale, is like this. Slate is useful for making roof tiles because its layers can be split into separate flat sheets.
Metamorphic rocks sometimes contain fossils if they were formed from a sedimentary rock, but the fossils are usually squashed out of shape.
There are several different types of rock in the circle. Take a look at each of them
Please message me with answers to the following questions:
Look closely at the undressed surface of the rocks.
1. Describe which rocks are the smoothest and roughest to the touch?
2. Taking the rock formation process into account, explain why this might be
Two of the standing stones are formed from different types of sandstone. Identify the two stones and have a close look at the layers of sand grains in the rock.
3. Describe which stone has lots of different sized grains and which has grains that are generally the same size?
4. Explain why you think the grains are different sizes when the base rock type is the same
Look closely at the granite standing stone and you will be able to see visible evidence of several accessory minerals on it. Sadly, there aren’t any crystals large enough to become gemstones!
5. How many different grains are visible in the rock.
6. The pink feldspar grains are particularly obvious in the rock. Measure the size of the largest grains
7. Optional –Photos of you at the site are very much appreciated.