You may be able to find free parking for one hour on this street, or the streets immediately off it, though it can be very busy.
I spotted this cladding whilst on Queen Street recently. Whilst looking into it I discoved that although it looks like Granite, it isn't really. It's worth viewing on a sunny day to see how it reflects the light, it can be very pretty to look at.
1) Describe the cladding - what size are the crystals you can see? What colours are present
2) Using your answer to (1), would you say the rock cooled slowly or quickly? Why do you say that?
3) What is the main feldspar present in Larvikite that contributes to it's colour
4) What is the name of the effect that causes the "sparkle" of the Larvikite when the light shines on it. Briefly, in your own words, describe how this happens.
5) Take a photo of yourself at GZ, or an identifying item, being careful not to reveal any of the answers to the questions.
Please submit your answers via message though the Geocaching website or by sending me an email - there is no need to wait for a response before logging your find.
Formation
Larvikite formed millions of years ago through the cooling and solidification of magma deep within the Earth's crust. This slow cooling process allowed for the growth of distinct mineral crystals, resulting in Larvikite's characteristic appearance.
Following its formation deep underground, Larvikite underwent a gradual journey to the Earth's surface propelled by diverse geological mechanisms. Surface conditions catalysed microscopic alterations within its feldspar crystals. Possessing a lamellar microstructure, which creates the colours that you can see when looking at the stone from different angles. This optical effect is called the Schiller (German for "shining" or "twinkle" effect or labradorescence, a phenomenon prominently displayed by Labradorite, another feldspar mineral. Simply put, as the light bounces of the tiny layers inside the crystals, appearing to create different colours.
The name originates from the town of Larvik in Norway.
Minerals Present
Larvikite is primarily composed of several key minerals, including feldspar, quartz, and feldspathoids. The predominant feldspar mineral found in Larvikite is known as oligoclase, which imparts the stone's signature bluish-gray hue. Quartz, often in the form of small grains or veins, adds depth and luster to the rock's surface.
Crystal Size and Cooling in Granite
In igneous rocks such as granite, the size of crystals is intricately tied to the rate at which the molten magma solidifies. Consider it akin to the process of cooling a liquid to form ice. Swift cooling leads to the development of minute crystals, resembling the rapid freezing of small water droplets in an ice tray. On the other hand, gradual cooling affords more time for crystal growth, resulting in larger, well-defined crystals akin to the formation of sizable ice crystals in a slow-freezing process.
If magma cools quickly, for example when lava erupts from a volcano, then many crystals form very quickly, and the resulting rock is fine-grained, with crystals usually less than 1mm in size.
If magma is trapped underground , it cools slowly because it is insulated by the surrounding rock. Crystals have more time to grow to larger size and crystals 2mm and larger can form.
For example, the picture below is Shap Granite, formed in the Lake District - the coin for scale here shows a slow cooling crystal as it's large in size.
