Bradford is a city of industry and many cultures, and if you look around there is much to see from a historical and geological perspective. Here we are here to look at the statue of William Edward Forster, a politician from the mid 1800s. We are here namely, to look at the plinth that the statue stands up.
The plinth is made up of two types of granite, pink and grey.
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 may form with or without 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. Granitic rocks mainly consist of feldspar, quartz, mica and amphibole minerals, which form an interlocking matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende) peppering the lighter colour minerals.
There are many EarthCaches which look at granite in detail, we are here to look for Xenoliths.
So what is a Xenolith?
Xenoliths are odd shaped, which are a different colour than the bulk of the granite rock. Xenolith is greek for a foreign rock, bascially it is a piece of rock trapped in magma. As explained above, granite is an igneous rock, this is a type of rock formed through the cooling and solidification of magma. A xenolith is a rock embedded in magma while the magma was cooling. As the molten material rises, it tears off bits and pieces of the magma pipe, or roof / wall of a pluton in which it was travelling in which it is traveling. These bits and pieces, trapped in the magma but not melting into it, become xenoliths. Crystals that are torn from the sides of magma pipes are called xenocrysts. As the magma flows out on to the surface of the Earth, or remains as a body within the crust, it is cooled, and various types of igneous rocks could be formed. Xenoliths usually have a different colour and density when compared to the surrounding rock, they can be small or large.
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 look around the plinth, which type of granite has the xenoliths in it (is it the pink granite or the grey granite)?
2. H ow are the xenoliths different from the granite, in terms of colour and texture?
3. On one aspect of the plinth is a leaf shaped xenolith, please measure how long it is, and how wide?