At the given coordinates is a large granite stone, a common rock seen frequently in many places in our everyday lives. Its popular uses include kitchen benchtops, grave markers and awesome EarthCache ideas! However, this one may be different to what you are familiar with.
Most people would know that granite has a lot of grains and minerals, the most common found in granite are:
♦ Mica, most commonly made up of biotite and muscovite.
♦ Hornblende
♦ Quartz
♦ Feldspar
All the above are formed by cooling magma deep beneath the surface, either by intense pressure and heat or by crystallisation.
(source: geologyin.com)
However, not all granite specimens turn out as they do in the picture above. A variation of granite known as leucogranite has little to no mica or hornblende imbedded into the stone.
This is because leucogranite is formed by a different process to regular granite. When magma cools down beneath the surface, the hot liquid solidifies into granite. This newly created rock is then uplifted to the surface as volcanic mountains get eroded away.
However, leucogranite is unique in that it forms by the melting of clay sediments. This occurs in the upper crust, where the heat is less intense. The melted clay goes through a process known as metamorphism, a transition of existing rock to a rock with a different mineral composition and/or texture.
The case gets interesting due to the fact that leucogranite still contains feldspar and quartz, despite being formed in similar processes as mica and hornblende.
Logging requirements:
Observe the granite at the given coordinates and answer the following questions:
1. Can you see feldspar amongst the rock? If yes, describe the texture, crystal structure and size.
2. Can you see any quartz amongst the rock? If yes, describe the texture, crystal structure and size.
3. Can see you any evidence of the metamorphism process left behind in the stone?
4. Why do you think there's feldspar and quartz in the stone but not mica and hornblende?
5. Take a photo of you, your stamp or personal item with the granite rock in the background.
Please send answers via the Geocaching message centre or to my email, answers posted in the logs will be deleted.
You can log the find immediately, if answers are supplied to CO within 14 days.
Happy caching!
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