Look around you, and you see colours, and we tend to take colours for granted, but what makes these colours? Now this is not an anatomy or physiology lesson, but one which talks about the minerology of colours.
Everything is composed of base factors, such as minerals, and it is these minerals that give stone their appearance. The co-ordinates take you to a feature below your feet in Halifax. The feature is made out of granite, which is not native to Halifax or the Yorkshire and Lancashire regions. In the Uk, there is granite to be found in the South West of Scotland and in the Highlands, with Aberdeen having the name of the Granite City. It has been quarried in many a place, though the quarries near Dalbeattie have provided granite sets for places such as the docks in Liverpool.
So what is 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 with or without crystallisation either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Intrusive rock forms within the crust from the crystallization of magma. As the magma pushes up from deep, it eventually slowly cools into a solid, and forms rock. An intrusive rock is any form of igneous rock that forms within the crust of the planet. Large areas of magma that solidify underground before they reach the surface are known as plutons .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.
The Minerology of Granite Colours.
The different coloured minerals in a granite, are mainly due to the original source of molten rock that cooled to form the granite. For example of the molten rock was abundant in potassium feldspar , you are likely to have a red / salmon pink coloured granite.
So what mineral gives what colour?
Quartz – typically milky white colour.
Feldspar – typically off-white colour.
Potassium Feldspar – typically red/ salmon pink colour.
Biotite – typically black or dark brown colour.
Muscovite – typically metallic gold or yellow colour.
Amphibole – typically black or dark green colour.
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 tell me what feature the granite cobbles make?
2. Please tell me which part of the feature has a granite which has greater proportion of amphibole. What is your rationale for this?
3. Looking at the whole feature please tell me what minerals are present here in the granite.
4. What does the granite feel like compared to the nearby flags?