In Curzon Square there are a series of benches constructed from granite. The bench at the posted coordinates has some embedded materials that do not look like the rest of the granite that surround them. These "foreign" materials are called xenoliths. You will learn more about xenoliths in this Earthcache
In order to receive credit for this Earthcache, please send a message with answers to the following questions:
1. How many granite benches in total are located in the square?
2. There are two xenoliths on the grey side of the bench at the posted coordinates. Describe their shape, color, and length.
3. Based on your observations of the bench, which of the following statements is most likely true?
A. The blackish and grey granites composing the bench were quarried from the same rock formation. Explain why.
B. The blackish and grey granites composing the bench were quarried from two different rock formations. Explain why.
4. In your online log, please post a photo of yourself or a personal item/caching name with the entrance to the square in the background. 
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.
The Granite Benches
Granite is a popular choice for public seating due to its durability, resistance to weather, and aesthetic appeal. Benches made from granite are often designed to be both functional and visually appealing.
One of the granites used in the Curzon Square benches looks black in color. While granite can appear black, it is typically composed of dark minerals like biotite, hornblende, and amphibole. The term "black granite" is often used for simplicity, even though true granite does not contain black minerals.
How is granite formed?
Granite, an igneous rock, is formed from the slow cooling and solidification of magma deep underground, which allows large crystals to develop. This process typically occurs in magma chambers beneath the Earth's surface, often associated with tectonic activity including zones of rifted continental or oceanic crust, and zones of collision between continents and oceanic crust.
What determines granite’s color?
The color of granite is primarily determined by the types and proportions of minerals it contains. Here are the key minerals and their typical colors:
- Quartz: Usually colorless or white, but can also appear gray or smoky.
- Feldspar: Can be white, pink, or various shades of gray. The presence of potassium feldspar often gives granite a pink or reddish hue.
- Mica: Includes muscovite (light-colored) and biotite (dark-colored, often black or dark brown).
- Hornblende: Dark green to black.
- Biotite: Dark brown to black.
- Other Minerals: Trace amounts of other minerals can also influence color, such as magnetite (black), garnet (red to brown), and tourmaline (various colors).
Xenoliths
Xenoliths in granite are formed when magma, which is molten rock, envelopes fragments of older rock as it moves through the lithosphere. These fragments are unrelated to the granite itself and are often pieces of older rock incorporated into the magma while it was still fluid. Xenoliths can form through various mechanisms, such as being detached from the margins of a magma chamber, torn loose from the walls of an erupting lava conduit, or picked up along the base of a flowing lava on the Earth's surface. When the magma cools and solidifies into granite, these embedded rock fragments become xenoliths.
Examples of xenoliths in granite:
- Peridotite Xenoliths: These xenoliths are often green, contrasting with the lighter, granitic host rock.
- Quartzite Xenoliths: These are common in some granitic intrusions and can be identified by their distinctive glassy appearance which contrasts with the surrounding granite.
- Gneiss Xenoliths: These xenoliths are derived from metamorphic rocks, specifically gneiss and they can appear as dark, elongated or rounded fragments within the granite.
- Mafic Xenoliths: Mafic xenoliths, such as those derived from basalt or gabbro, can also be found in granite. These xenoliths are typically darker and denser than the surrounding granite and may have a more fine-grained texture.
Quartzite xenolith in granite
Xenoliths in granite are valuable for geologists as they offer a window into the conditions and processes that occurred deep within the Earth, which are otherwise inaccessible. By studying these inclusions, scientists can better understand the geological history and the formation of granitic rocks.