Please read the whole of the cache listing and answer the questions below.
I read every single email and always respond so please send a message, or email, with answers to the questions below, to log your find.
You may log your find at the same time since the answers are pretty easy.
There is parking close by and the pavement is even but not level around the location.
For this cache I’d like you to turn your attention to the drinking fountain just outside the bowling club.
You will be asked questions about the colours of the different granites used.
What is Granite?
Granite is an intrusive igneous rock with large crystals (minerals) easily seen by the naked eye. Granite colours are most commonly pink, white, variations of grey and black. However, it's important to note that some stones marketed as black 'granite' are in fact likely gabbro as granite must contain at least 20% quartz within a rock to make it technically granite.
The colours of different granites range the spectrum from white to black to pink, but what makes a single rock type so variable? Here we will discover what makes each granite a different colour, what that tells us about its mineralogy and origin. You may be an amateur geologist, just curious, or looking to identify what you are looking at. Regardless of the reason, you'll be amazed at the vast varieties of different granites.
Granite is one of the most commonly known types of rocks, used in everything from buildings to sculptures. It has been used for thousands of years and is regarded as a symbol of status, strength, and durability.
Granite is an igneous rock so, let me explain what exactly an intrusive igneous rock is:
An intrusive rock means that molten rock cooled within the crust and was never expelled as molten rock. The gradual cooling of molten rock is imperative to create the large crystals of a singular mineral that we see in granites. With time, there is differential lithification or solidifying of molten rock dependent on chemical makeup, this allows for different types of minerals to form at different periods of time and alter the final resulting granite. Therefore, the size of individual crystals is in proportional to how slowly the molten rock was cooled. Extrusive rocks cool during a volcanic eruption and allow no time for orientation of minerals, creating a homogenous looking rock with no discernible crystals.
An igneous rock is a rock that has solidified from molten rock so it has been heated, usually by intense pressure and then cooled as the pressure is released. This cooling can be quick or slow depending on the conditions. This is in comparison to the two other major types of rock, sedimentary and metamorphic but were not dealing with those at this cache.
What Determines Granite Colours?
This is the focus of this cache
Granite is a made up of minerals and rocks, primarily quartz, potassium feldspar, mica, amphiboles, and trace other minerals. Granite usually consists of 20-60% quartz, 10-65% feldspar, and 5-15% micas (biotite or muscovite). The minerals that make up granite give it the unique colours we see in different types of granite at this location.
The relative proportion of different coloured minerals that make up a granite is largely due to the original source of molten rock that cooled to form the granite in the first place. If the molten rock was abundant in potassium feldspar, the granite is more likely to take on a salmon pink colour. On the other hand, if the molten rock is abundant in quartz and minerals that make up amphibole, you will likely get a black and white speckled granite commonly seen on countertops.
Here are some general trends in the colour of a granite which has predominant mineral within its make-up.
Quartz - typically milky white colour
Feldspar - typically off-white colour
Potassium Feldspar - typically salmon pink colour
Biotite - typically black or dark brown colour
Muscovite - typically metallic gold or yellow colour
Amphibole - typically black or dark green colour
The combination of the minerals above make up most of the colours we typically see in a granite.
Here is a little more detail on some of the colours.
White granite is composed primarily of quartz (milky white) and feldspar (opaque white) minerals. The small black specks in the granite above are likely small amphibole grains. This could be due to a lack of chemical components needed to form amphibole, or the cooling process was not amenable to formation of amphiboles.
Pink coloured granite is a result of an abundance of potassium feldspar within the granite. You will see small specs of milky semi-transparent quartz, dark brown/black amphibole, and opaque white feldspar. However, in a granite that is mostly pink the primary mineral is potassium feldspar.
A black and white granite will have equal parts quartz, feldspar, and amphibole, making a speckled black and white granite. This is one of the most common types of granite and one that is most commonly seen used for granite countertops.
Red granite is a variation of the pink potassium feldspar abundant granite, where the k-feldspar takes on a redder than pinker colour. Also, you can get red colouring from iron oxide in hematite grains or inclusion within feldspar, essentially the same process that makes rusted metal ruby red coloured.
Black, blue or green ‘granite’ are almost certainly not in fact granite at all.
Black ‘granite’ is in fact gabbro, a mafic intrusive igneous rock similar to basalt.
Blue ‘granite‘ will most likely be Larvikite, an igneous variety of monzonite, or Anorthosite, a rock that contains abundant blue labradorite.
Green granite is most likely actually a green variety of marble, which gains its colouration due to inclusions of serpentine.
Right, so having bombarded you with a lot of information you need and some that you don’t I’d like you to either message or email the answers to the questions below to claim a find.
- Please describe the stone used in the construction of the water fountain, concentrate on the colours.
- Please tell me which parts of the structure are made from which types of granite tell me the predominant minerals in each section and explain your reasoning.
- Please tell me the name of the man on the plaque and why was he commemorated?
If you feel willing and able you are welcome to include photos close to the cache location but DO NOT include any picture of the stones.
Thank you so much for attempting this cache, if it’s a weekday summer’s day I may be on the bowling green, pop in and say hi.
Happy caching
treboR