(Hide #995) Don’t Take this EarthCache for Granite EarthCache

—————————————————————————————————————————

(Hide #995) -> Don’t Take this EarthCache for Granite

A little bit of Background

At GZ, you will notice 4 large granite structures, that make up the art piece, designed by David M. General, titled “The Eagles Among Us”.  The artwork, installed May 2014, consists of four, nine-foot-high granite eagle figures inscribed with symbols and text arranged on a circular plaza. The artist uses interpretations of the cultural traditions of the Haudenosaunee and Anishinabek communities to address the theme of healing and reconciliation. The work was commissioned as part of the City of Hamilton’s War of 1812 Bicentennial commemoration.

Now for the EarthCache:

Granite colours range the spectrum from white to black to pink, but what makes a single rock type so variable?  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.

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.  To be considered granite, the rock must contain at least 20% quartz.

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 of minerals and rocks, primarily quartz, potassium feldspar, mica, amphiboles, and trace 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 - 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. Now, let's break down the different types of granite with an overview of what gives them their colour.

White granite (Credit: geology.com)

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).

Black Granite

"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. 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.

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

The above 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 (Credit: eurasian.com)

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.

Blue Granite

You may find advertisements for blue granite but this is also almost certainly not granite. One potential is that the rock is actually 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.

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. It could also be a green variation of soapstone, mislabeled as granite. 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.

Now for the Hard Part

Before claiming this EarthCache as a find, please submit the answers to the following questions to the CO at the top of the cache page.  Found it logs, without submitted answers, will be deleted.

1) Based on the reading, I hope you read the information, which of the 4 structures at GZ, would you say are an intrusive rock?  Which are extrusive?

Now, get your spectacles out, you are about to become a "Granite Inspector".

(Just because they say it’s granite, is it really granite?)

Take a close look at each one of the four “granite’ sculptures at GZ.  Use the names on the bottom of the sculptures: Respect, Friendship, Well Being”, and “Peace” to answer the following questions

2) From the information on the cache page, do you believe all four sculptures are granite.  Which ones are?  Which one are not?  Explain your reasoning

Respect:  Granite or Not Granite, Why?

Friendship:  Granite or Not Granite, Why? 

Well Being:  Granite or Not Granite, Why?

Peace:  Granite or Not Granite, Why?

3) Using the information on the Cache page, describe the percentage of each mineral present in the sculptures.

Respect contains:

Friendship contains:

Well Being contains:

Peace contains:

Optional Questions (Please include in your Found it Log)

4) Since the theme of this art piece is 'Healing and Reconciliation', look carefully at the artwork, and what you just learned about the rock samples at GZ, to explain which one you connect with the best?  Be sure to explain why.

5) Photos are always welcome, but not required to claim this Earth Cache.

Hope you enjoy this EarthCache, to learn more, you may want to check out my source articles:

https://www.forbes.com/sites/trevornace/2016/06/05/granite-colors-white-black-countertops/?sh=11c021957b98

https://en.wikipedia.org/wiki/Granite

https://geology.com/rocks/granite.shtml

https://www.hamilton.ca/attractions/culture/battlefield-park-public-art-project