To claim a find for this EarthCache you must visit the location given and make some observations. Then you must find the answers to the questions below and either email (for a quick reply) or use the geocaching message system, to send them to me.
I reply to email quickly and will endeavour to reply to the messages within a few days.
This memorial is made up of a top section of heavily weathered yellow sandstone and two different types of granite below, one for the columns and urn and another type of granite for the base.
What you have to do is find out why the different stones, both of which are granite, are different colours.
Below you will find out why these stones are different colours.
How granite forms
Granite is formed by the intrusion of igneous rock. Intrusion means that the molten rock cooled within the Earth's crust and was not expelled to cool quickly. Granite has large crystals which can easily be seen by the naked eye and typically can range from 1mm in diameter to 10mm, however if the granite cools slowly the crystals can be much larger, up to several cm in diameter. Granite colours range from white all the way to black with common colours being pink, white, oranges and many shades of grey. Granite must contain at least 20% quartz to classified as such and some of the darkest stones which can be confused with granite, are in fact gabbro, which is a dark crystaline igneous rock composed mainly of labradorite and augite .
When it forms the mineral content of the molten rock will have an impact on the final colour of the resulting stone. The relative proportion of these different coloured minerals in a granite, is largely due to the original source of molten rock that cooled to form it.
Here are three different colours that granite can be and what type of minerals cause the difference in colours.
White granite
If the molten rock is abundant in quartz you will most likely get a mainly white granite with black and white speckles. The white crystals with be larger than the the small black flecks so the base colour will look white. This type of granite is typically milky in colour, it almost seems you can see into the rock because doesn't have a block colour and is mainly white.
Green granite
If you were to come across a stone which you think is green granite, it is more likely that the stone is a variety of marble which has its green colourations because of inclusions of serpentine. Another possibility is that it is a type of soapstone. Green coloured actual granites are rare but can be found if the stone has amazonite which is a green variety of feldspar. It is unlikely that a green granite would be used for a public structure because of its rareness and consequent cost.
Pink granite.
Pink coloured granite will be a result of an abundance of potassium feldspar within the granite itself. You may also see small specs of milky semi-transparent quartz, these crystals can also be dark brown or black and will be the result of an opaque white feldspar. However, in a granite that is pink the primary mineral will be potassium feldspar.
Questions.
1) Describe the two types of granite, include the crystal size, shape, colours, and finished state of the stone.
2) Tell me the predominant mineral constituency of the two granites with explanations of your conclusions.
Thanks for attempting this cache.
Please send your answer using email or the message system, or of course you could personally deliver your answers if we meet up.
If you wish to include a photo, that's fine but don't include the memorial in your photo, please.
Thanks
treboR