The geology of the Halifax area is predominantly that of sandstones and mudstones, all laid down in the Carboniferous period. Look around the town and the surrounding countryside and you can see many a good example of sandstone outcrops. If you look into the heart of the town there is much to see and learn about in the terms of geology.
Stage One - The Start.
This EarthCache starts just outside the gate to Piece Hall on Westgate. From here enter in the vast public space of the Hall itself, which is a wonder to see and explore.
Stage Two Granite Bench
Here there is a bench made out of granite. 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 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. 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. This type of granite is Alpendurada Granite which is from Portugal.
Look at the bench (unless someone is sat on it - in that case do the other stages and come back 
, it has an odd shapped bit, which is different to the rest of the rock forming the bench. What you can see is a Xenolith. 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.
TASKS AT STAGE TWO
Please measure the xenolith, how wide is it?
Is it regular or irregular in its shape?
What colour is it?
Stage Three - Cobbles
There are two types of rocks here, granite, which we have talked about above, and Blue Limestone. Limestone is a sedimentary rock, which was formed when sea creatures died and fell to the bottom of a tropical shallow sea, there shells formed sediment, which over millions of years, was compressed into layers and the rock known as limestone. The limestone used here comes from Ireland. At times fossils, which are the remains of the sea creatures can be seen in some type of limestones.
TASKS AT STAGE THREE
Please touch the limestone cobbles, how do they compare to the granite cobbles?
Which stone makes up the the greatest proportion of cobbles?
Stage Four - The Pavement
The pavement is made out of sandstone, namely Pennant Sandstone, which originates from the Forest of Dean. Sandstone is a sedimentary rock. Sediments, mainly sands, silts and muds, were eroded from hills and were swept into vast river deltas and lagoons. The sediment settled to the bottom as the water slowed down in the deltas and lagoons.
Now, colour plays an important part of our lives, it helps us to define and describe objects. It is the same with geology, and indeed can give us a hint about what it is made of. In the case of standstone, the colours will usually be tan or yellow (from a blend of the clear quartz with the dark amber feldspar content of the sand). The addition of Iron Oxide in some sands gives a reddish tint to the sand, while additional manganese gives a purplish hue.
TASKS AT STAGE FOUR
Please look around, at the sandstone slabs.
What colours can you see?
What caused these colours?
This being an EarthCache, in order to log it, I ask that you complete the tasks. 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.