In order to claim a find for this EarthCache you will need to visit the location given, make some observations and answer some questions.
You may use the message system to send you answers to me or email if you wish a quicker reply.
I will usually respond within a few days but you don't need to wait for a reply to log your find.
Finally if you wish to include a photo of your visit that's fine but not a requirement.
For this cache you are concentrating on the pillars of stone used to 'face' the building which is currently a bank. You do not need to approach the building too closely in fact the colour and texture of the stone is quite apparent from a few metres away.
The questions for this cache is simple.
Describe the texture and colour of the decorative rock used in the window frame and uprights and tell me what type of rock it is, with an explanation of your reasoning.
If you need help identifying the stone please read on
At the location given the window frames and uprights are faced with a green stone, below are three types of stone which can be green with explanations of how they form, what they look like in a cut or industrial form and why they are green
Slate
Firstly a very fine grained sandstone or more likely mudstone must be formed, probably in a regular, slow flowing delta of a river. This alone takes millions of years before we can start the slate making process. Once the rock is well formed earth movements on the mudstone causes the rock to be put under immense pressure, which heats the rock and causes the plates to line up parallel to each other with fine bedding planes which will enable resulting slate to split into sheets easily.
The colour of the resulting slate depends on the chemical and mineral composition of the donor rock. Slates range from green, which would be chlorite rich, to black or grey, purple and even red because of carbon, haematite and iron oxide deposits respectively.
Slate is generally consistent in colour across the whole rock, it is unlikely to see wide variations of colour in a piece of slate and you would see no crystals at all.
Green granite
Granite is a stone which forms when the molten rock is expelled from the heart of a volcano but does not make it to the surface to cool quickly. It generally cools slowly underground and forms crystals which can be seen with the naked eye. If you were find a stone which appears to be 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.
If you were to see green granite here it is likely that you would be able to see many crystals in the shape of bubbles or ovals up to 10mm in diameter in a base material with many smaller specks of white or black. The whole sheet seen would be of a similar consistency looking like bubble wrap in rock, though not quite as regular.
Green marble
Like slate, before the formation of marble we need a donor stone. This time a limestone base is needed which forms in a creature rich environment. The ancient tropical sea this stone forms in is teeming with creatures that sink to the bottom as they die and their calcium rich skeletons or shells pile up and compress to form limestone over millions of years. Then comes the metamorphic process that changes the stone to marble. Intense pressure and heat, probably from Earth's tectonic movements cause the stone to almost liquefy and as impurities of minerals seep into the mix as it cools marble is formed. A green colouration of the stone is often due to serpentine resulting in a magnesium rich limestone or silica impurities. Because of the unequal distribution and lack of full liquification and resultant mixing of the materials, marble is usually marbled (sorry) or unequally mixed, resulting in a rock which could have huge crystals, or a wide range of colours and shapes in the visible surfaces.
Right so that's three types of green rocks which you might find used for structural decoration. Which one has been used here?
Thanks for attempting this cache, hope you found it interesting and informative.
treboR