The geology of the Calder Valley is carboniferous from a time when this part of Yorkshire was covered by a vast river delta. Sediment was washed down from far to the North and deposited as sandstone, siltstone and millstone grit. But there are enough EarthCaches which describe these types of stone. We are here to look at something different, namely some different types of igneous rocks, such as Granitic rocks and Gabbro. Normally you would have to travel as far as the Lake District, North Wales and the Galloway Hills in Scotland to see types of Igneous rocks, but this EarthCache gives yourself the opportunity to do this without having to worry about a long trek into the mountains or weekends away in some remote spot.
It is meant to be accessible for the majority of Geocachers so you can come away having learnt something.
So what are Igneous rocks?
Igneous rocks are formed from the solidification of magma which has been formed deep within the Earth. Their appearance differs depending on their content, feel and colour. What we have here are some different types of Granitic rocks and a Gabbro.
Granite is a common type of igneous rock. Igneous rock is one of the three main rock types , the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Igneous rock is formed by crystallisation either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Granite can be white, pink, or gray in colour, depending on their mineralogy. The shades can also vary and the crystals can be different sizes. Granitic rocks mainly consist of feldspar, quartz, mica, amphibole and biotite minerals, which form an interlocking matrix of crystals.
Feldspar - this is typically an off-white colour, but it can have a salmon pink colour and this is known as potassium feldspar. This is often the most abudant in a Granitic rock which can be why the rock may appear white with dark spots or pink with dark spots.
Quartz - this is one of the most common minerals in the world and is formed from silicate. It can be a variety of colours including milky white, rose and clear.
Mica - this is a shiny silicate material with a layered structure found as minute scales in granite and other rocks. It can appear to be white, colourless and in certain lights can appear to be silver.
Amphibole - this is typically black or green colour.
Biotite - this is used for a large group of black mica minerals which are generally found in igneous rocks, it tends to black / brown in colour.
Differing amounts of the above can contribute to the different colour of granitic rocks.
Gabbro is an Igneous rock which is formed from the slow cooling of magnesium and iron rich magma deep beneath the Earths crust. It is a coarse-grained, dark-coloured rock. It is usually black or dark green in colour.
Basalt is a dark coloured, fine grained Igneous rock. It commonly forms as what is known as Extrusive rock in bodies such as lava flows which means it is formed after being forced out of an underground magma chamber, ie extruded on to the surface. Granite and Gabbro, however are Intrusive rocks and Granite can be formed in plutons which are vast areas of magma and under the Earths crust, commonly the Granite found in South West Scotland around Dalbeattie and the Loch Doon area are plutonic Granites. A lot of the Granite which is used as building stones in urban areas in the UK comes from South West Scotland, Aberdeen and Cornwall.
Now its time to have a look around the monuments you will find here. There are four monuments I would like you to look at. At the published coordinates you will find 3 of them side by side. When facing the rear of the church, lets number them from left to right (1 to 3). At the rear of the church, very close to the building, you will find number 4 (it has the words Jesu Mercy on it to help you ensure you are looking at the right one). There are paths between these monuments and this cache can be completed without leaving the paths. Please be respectful of the location when undertaking the tasks, and respectful of other users (if anyone is, about which is rare).
First please visit monument 1.
1 - Please tell me what overall colour the memorial is (you will need to use dark, light or medium to answer this question). Please look closely at the monument and tell me what minerals are present?
Please now visit monument 2.
2 - Using the above information what type of Igneous rock is this and what is your rationale for your answer. Compared to monument number 1, would you say the crystals are bigger or smaller in general?
Please visit monument 3.
3 - Whilst looking at the Eastern face of the cross pay close attention to the far left part of the cross and you should be able to see a mica crystal which stands out as being larger than those around it. What colour is this crystal? Please describe the size and shape of this crystal in terms of milimetres.
4 - On the ground to the right of monument 3 there is a flat-laying stone. Please tell me what words are engraved on this stone.
Please visit monument 4.
5 - What colours are in the granite? Why is it this overall colour?
6 - Please include a photo of yourself (or a part of yourself, or something distinctive which belongs to you, if you don't want your face on the photo) featuring one of the Gargoyles which can be found all around the outside of the church. Please do not include the monuments in your photo.
Answers can be sent to me either by e-mail or via the message centre. Please feel free to log your find at the same time as you send answers - if there are any issues I will contact you.