I finally made it to the Titanic quarter, and after a quick visit to the museum, spotted these contrasting stones as we looked for somewhere to eat.
The stones are used to contain flower beds, but also provide seating. The lower, wider, more common stone, is Stone A. The taller, thinner stone that breaks up these sections is Stone B. The image above has altered colours, but enables you to more easily identify which sections I'm referring to.
1) Which stone is mafic and which is felsic? Explain your reasoning based on their appearance.
2) Which of the three rock types (granite, basalt, or gabbro) is Stone A most likely to be? Why?
3) Which of the three rock types (granite, basalt, or gabbro) is Stone B most likely to be? Why?
4) Take a photo of yourself at GZ, or an identifying item nearby - please do not include answers in this photograph.
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.
Understanding Mafic and Felsic Rocks
Rocks are broadly classified based on their mineral composition, which often correlates with their colour and density. This classification helps us understand the conditions under which the rocks formed.
Felsic Rocks: These rocks are rich in lighter-coloured minerals such as quartz, feldspar, and muscovite. They are typically light in colour (pink, white, grey) and have a relatively low density. "Felsic" is a portmanteau of "feldspar" and "silica" (referring to quartz). They generally form from magmas that are rich in silica.
Mafic Rocks: These rocks are rich in darker, iron and magnesium-rich minerals such as pyroxene, amphibole, and olivine. They are typically dark in colour (black, dark grey, green) and have a relatively high density. "Mafic" is a portmanteau of "magnesium" and "ferric" (referring to iron). They generally form from magmas that are low in silica but high in iron and magnesium.
Types of Igneous Stones
Igneous rock is a popular building material in public areas - it's extremely hard wearing and often attractive. Various different types of igneous stones are often used:
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Granite: A common intrusive felsic igneous rock. It is typically light-coloured with visible interlocking crystals of quartz, feldspar, and mica. It forms from slow cooling of magma deep beneath the Earth's surface.
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Basalt: A common extrusive mafic igneous rock. It is typically dark-coloured and fine-grained (crystals are too small to see with the naked eye) due to rapid cooling of lava on the Earth's surface.
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Gabbro: A common intrusive mafic igneous rock. Like basalt, it is dark-coloured, but unlike basalt, it is coarse-grained (crystals are visible) because it cools slowly deep beneath the Earth's surface. Gabbro is the intrusive equivalent of basalt.