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.
This EarthCache is concerned with the variety of stones that are at your feet in the alleyway between the buildings. There is a variety of stones used to make this pavement and I will explain how each stone if formed, that it looks like and how to identify each type.
Please note you are looking at the natural stones NOT the bricks in the main pathway.
Then you have a simple question to answer.
Please describe each of the 4 types of stones including, colour, texture, shape of the block and any visible crystals, oh and remember to tell me which is which.
The four stone types used for this pavement are;-
Basalt
Red Granite
Pink granite with flow banding
White marble
If you need some information about how to identify each one, read on.
Basalt
Basalt is a common igneous extrusive, which mean volcanic, rock. It is usually composed of mostly minute grains of plagioclase feldspar, usually labradorite, and less than 20% quartz. Basalt is most commonly dark grey or black in colour. The rock itself is formed when basaltic magma cools quickly because it is very close to or on the surface of the earth, when it is extruded. When such magma flows it is quite thick, gloopy, and gas cavities are almost absent. This creates a dense material which can be cut and carved. It is most likely to be black which when unpolished and weathered has a tarmac look to it but when cut and polished can be mirror like
Pink or red granite
Granite is a rock formed by the intrusion of igneous rock which means that the molten rock cooled within the Earth's crust and was not expelled to cool quickly like the basalt described above. Granite has large crystals which can easily be seen by the naked eye and typically can range from 1mm in diameter to 10mm. The slower a mineral rich substance cools the longer it has to grow its crystals, so they can be larger than 10mm. In this sample there are many larger crystals than 10mm indicating that it cooled slowly
Granite colours range from white all the way to black however the most common colours is pink or red and that's what you will find here. 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 crystalline igneous rock composed mainly of labradorite and augite.
Pink or red coloured granite will be a result of an abundance of potassium feldspar within the granite itself the more the redder the granite. 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.
Flow banding
Flow banding is a term used by geologists to describe bands or layers that can be seen in rock that formed from magma. Volcanic rocks are usually made up of fine crystals but can show structures causes during the movement of the rock during its eruption which can be intrusive or extruded. If a rock is stationary during its cooling the crystals will have time to form round well defined structures, or long needle like crystals, but if the rock is under pressure and moving whilst it cools the crystals will be sheared as they cool and this process is called flow banding. Because of this process it can be difficult to identify the individual crystals in the resulting rock and the structure will look smeared like jam and butter mixed together and spread on bread with a knife.
White Marble
White smooth rock with veins which can be polished is usually a type of marble. White marble is the result of metamorphism of limestone and the characteristic swirls and veins in the rock is because of various mineral impurities such as mud, salt, sand , or other minerals, as it formed. The metamorphic process is caused when the limestone is heated and squeezed by natural processes and this makes the grains recrystallise. It is often possible, if you look carefully, to still see fossil embedded in the rock held together by a calcite matrix. The purer the donor limestone to cleaner marble you will get.
OK so that tells you about the four types of rock used to make this pavement, all you have to do is tell me which shape is which and why you think that.
The pavement here is quite worn and weathered but if you go inside the shopping complex you will see what can be achieved when these types of rock are highly polished, the differences are quite striking.
Thanks for attempting this cache.
treboR