Welcome to my Earthcache! An Earthcache is a special type of geocache where there is no container to find - instead you are looking for a unique geological feature of the area and need to answer questions, as well as posting a picture, in order to claim the find. The goal of this Earthcache is to educate visitors about granite, it's development, it's composition and it's uses. All observations can be made from the sidewalk at GZ in Victoria Park. This cache is wheelchair accessible.
EARTHCACHE REQUIREMENTS
As with all of my ECs, I am not looking for PhD thesis level responses, but I am hoping that you take some time to enjoy the area and learn something new. Please include a list of all cachers with your answer, if answering for more than one caching name. There is no need to send individual answers.
To claim a 'find' for this Earthcache you must answer the following questions and send your answers in a message or email to the owner using the link at the top of the page. You can log your find with a photo at GZ. Send your answers to the tasks. I will be in contact if there is a problem, no need to wait for a response as long as the required photo is included in your log.
Observational Task
At GZ, you will be standing in front of a large marble fountain, built in 1892 and donated to the people of the City of Brantford. This fountain was donated by J.K. Osborne, who was a vice-president of A. Harris, Son & Co. and Massey-Harris Co. Ltd., forerunners of Massey-Ferguson Ltd. You will be observing the various marbles that make up this fountain to answer the questions below.
Questions to Answer
1. Observe the various colours of the fountain. There should be at least three different colours of granite visible in the fountain. Based on the reading and your observations, which colour(s) would you say are an intrusive rock? Which colour(s) are extrusive rock?
2. From the information on the cache page, do you believe all three colours are granite? Which one(s) are and why? Which one(s) are not and why?
3. Using the information on the Cache page, which colour has the highest percentage of feldspar? Which one has the highest percentage of quartz? Which one has the highest percentage of biotite?
4. Mandatory: Include a photograph of yourself, your GPS, a signature item, thumbs up, etc at the fountain. You do not need to show your face in the photo, but your photo must be unique to you. If you are caching with a group you can use the same photo, but each log must upload a photo.
Geology Lesson:
Granite colours range the spectrum from white to black to pink, based on its composition. Granite is one of the most commonly known types of rocks, used in everything from buildings to sculptures to headstones and (apparently) fountains. It has been used for thousands of years and is regarded as a symbol of status, strength, and durability.
What is Granite?
Granite is an intrusive igneous rock with large grains (minerals) easily seen by the naked eye. Granite colours are most commonly pink, white, variations of grey and black. Green, Blue and Purple are also possible. To be considered granite, the rock must contain at least 20% quartz. This quartz is often what gives granite its reflective nature.
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.
What Determines Granite Colours?
Granite is a conglomerate (meaning ithas many parts, cemented into one rock) of minerals and rocks, primarily quartz, feldspar, mica, amphiboles, and trace amounts of other minerals. Granite typically contains 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.
The relative proportion of different coloured minerals in a granite is largely due to the original source of molten rock that cooled to form the granite. 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.
Granite Colours:
- Quartz - transluscent white colour
- Feldspar - translucent or opaque off-white colour
- Potassium Feldspar - transluscent or opaque salmon pink colour
- Biotite - a type of mica, typically black or dark brown colour
- Muscovite - a type of mica, 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. Now, let's break down the different types of granite with an overview of what gives them their colour.
White granite
White granite is a granite that 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.
If you see a rock that is 100% white, it is not granite but more likely a man-made rock that is created to look like granite or a quartz (quartzite).
Pink Granite
Pink coloured granite is a result of an abundance of potassium feldspar within the granite. You can see small specs of milky semi-transparent quartz, dark brown/black amphibole, and opaque white feldspar. However, in a granite like the one above the primary mineral is potassium feldspar.
Black And White Granite
This granite appears to have equal parts quartz, feldspar, and amphibole, making a speckled black and white granite. This is one of the most common types of granite.
Red Granite
Red granite is a variation of 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.
Is it granite or not?
Blue Granite
You may samples claiming to be "blue granite", but this is more likely to be Larvikite, an igneous variety of monzonite and sometimes referred to as "blue granite" despite it not being granite. Another common alternative is Anorthosite, a rock that contains abundant blue labradorite and is sometimes sold as blue granite.
Black Granite
Pure "Black granite" is commonly seen in commercial rock, but it is not granite at all. Granite must be at least 20% quartz, which means an all black rock is not a granite unless it also contains at least 20% quartz and other minerals present. Most commonly, black granite is in fact gabbro, an intrusive igneous rock similar to basalt. Gabbro is primarily composed of minerals pyroxene, plagioclase, and small amounts of olivine (dark green) and amphibole.
Green Granite
When advertised as green granite, often times the stone is actually a green variety of marble, which gains its green coloration due to inclusions of serpentine. Granites are not abundant in green coloured minerals, but there are a variety of different rock types that do contain green minerals in abundance. One very unusual way to get a green coloration is the inclusion of amazonite, a green variety of feldspar.
Granite has been intruded into the crust of the Earth during all geologic periods, although much of it is of Precambrian age. Granitic rock is widely distributed throughout the continental crust and is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents.It is believed that the granite that forms this statue was collected locally, in Northern Ontario.
This EarthCache has been prepared by a proud:
