Red Granite at Queen Victoria Statue
In the United Kingdom, intrusions of granite and related igneous rocks are present in a variety of localities, and range widely in geological age and origin. Differences in mineral composition and conditions of emplacement mean that British granites show a wide range of colours and textures.
This EarthCache will teach you about the special features of the Red Aberdeen Granite.
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1. Watch the observable mineralogy in the granite at GZ and describe the texture of the Red Aberdeen Granite at Queen Victoria Statue (little help: is the texture fine-grained or coarse-grained? Are there individual mineral grains visible?) If so, which mineral grains can you identify?
2. Rubing your hand over the granite surface. How do you classify it: extremely rough, rough, smooth, or polished?
3. The memorial column consists of two parts made of Red Aberdeen Granite: a granite slab beneath Queen Victoria's feet and the monumental base. Compare the two granites: Do you see any signs of weathering? Explain your observation in your own words.
4. Why do you think red Aberdeen granite was used instead of marble? What could be the main reason for this decision?
Take a photo of yourself with your GPS (or your GPS alone) at a recognizable part of the site.
What is granite and how is it formed?
Granite forms from the cooling of large magma bodies at depth in the crust, the slow cooling allowing the growth of large and interlocking mineral crystals. Compositionally, granites typically contain between 55-75% silica and are commonly pale coloured with medium to coarse grained crystals discernable to the naked eye. The interlocking crystals provide cohesion which adds strength and makes them very suitable for polishing without plucking of the grains. Finer grained granites were typically used for structural purposes (e.g. foundations or paving), while coarser grained and porphyritic (= those with large crystals usually of feldspar) varieties were valued for ornamental work. The predominance of silica and other relatively stable minerals in granite make it particularly strong and durable.
Uses of granite:
Because of its hardness and comparative cheapness in relation to marble, granite has been used for thousands of years for both internal and external features. It is commonly used outdoors in construction of buildings, bridges, paving, for monuments and indoors for items such as tile, countertops, stair treads and much more. It can be cut into virtually any shape, and is practically unscratchable.
Red granite appearance (in general):
From a distance, red granite looks reddish or pink. Here the granite is made mostly of the minerals feldspar and quartz. The feldspar gives this granite its red hue and the quartz crystals appear as a semi-clear gray or purple color. There are also small crystals of mica and other darker minerals which appear as specks in the rock. Many broken surfaces are flat and shine in the sunlight.
The "red Aberdeen granite," is a type of felsic plutonic rock typically 470 million years old, characterized by a distinct reddish color due to high iron oxide content. The color is caused by the presence of red orthoclase (K-feldspar).
Red Aberdeen granite is a rare, colored variety of the famous Scottish granite quarried in northeast Scotland. While the city of Aberdeen is primarily composed of the characteristic silvery-grey Rubislaw granite, pink and red granite varieties from the region lend a distinctive, warm appearance.
Key Characteristics & Uses:
Historically, this reddish stone was used for prestigious masonry and paving. Today, it is primarily available as decorative, angular aggregate (6-14mm) for, landscaping, driveways, and, resin-bound surfacing, appreciated for its, vibrant color, longevity, and, superior strength.
Appearance: Rich deep red or salmon-pink, often with flecks of quartz and mica.
Durability: Highly weather-resistant and hard-wearing; historically used for "fortress-like" buildings.
Aggregate Uses: Ideal for decorative garden borders, landscaping projects and drainage-efficient pathways.
The price: Red Aberdeen granite has always been a valuable granite, but significantly cheaper than marble.
Modern Applications: Commonly used in resin-bound systems to provide a durable and slip-resistant surface.
Varieties: While "Red Aberdeen" refers to local stone the term is sometimes used to describe similar pink-red granites such as Peterhead granite.
The observable mineralogy in the Red Aberdeen Granite at Queen Victoria Statue (Windsor Castle)
The statue on a red Aberdeen granite base at the foot of Castle Hill, Windsor was erected in 1887 in celebration of the queen's Golden Jubilee.
Primary Minerals of red Aberdeen granite:
K-Feldspar (Orthoclase/Microcline): The dominant mineral, giving the rock its red, salmon color.
Quartz: Abundant, often forming large, interlocking plates.
Plagioclase Feldspar: Generally albite or oligoclase, often intergrown with microcline.
Biotite Mica: A major dark constituent, often appearing in small, "fox-brown" grains.
Muscovite Mica: Present as smaller, intergrown plates with biotite.
Accessory and Secondary Minerals
Apatite, Zircon, Monazite, Magnetite, and Garnet: Common accessory minerals.
Macaulayite: A rare iron-aluminum silicate mineral found in the reddish, weathered granite of the Bennachie area.
Epidote and Barite: Found in microcavities within some red granite varieties.
Sericite and Kaolinite: Products of hydrothermal alteration or weathering, commonly affecting the feldspars.
Pyrite, Chalcopyrite, and Ilmenite: Found in certain, more altered or veined facies.
Petrography and Characteristics
Texture: Medium- to coarse-grained, typically with an interlocking crystalline structure.
Structure: Often massive, but can show foliation defined by aligned micas or biotite-rich schlieren.
Origin: The granite is sedimentary-derived, formed by the melting of metasediments during the Caledonian Orogeny (which was the major mountain-building event occurring roughly 490 to 390 million years ago (Early Palaeozoic), caused by the collision of Laurentia, Baltica, and Avalonia as the Iapetus Ocean closed. This multi-phase collision created Himalayan-scale mountains across the British Isles, Scandinavia, and Greenland, forming a key part of the supercontinent Pangea's assembly.
A brief digression on the topic of "weathering"
In geology and geomorphology, three main types of weathering are distinguished: Physical (mechanical) weathering, Chemical weathering and Biogenic (biological) weathering.
Note: Sometimes biogenic weathering is considered a subcategory of chemical or physical weathering, but it is often listed as a third, independent category.
Physical weathering, also called mechanical weathering, is the class of processes that causes the weathering of rocks without chemical change. The primary process in physical weathering is abrasion.
In geology, abrasion is the mechanical erosion and grinding of solid rock by the frictional action of rock fragments (wave debris) moved by water, wind or ice. Thermal stress weathering occurs when temperature changes cause the expansion and contraction of rock. Frost weathering occurs when water seeps into cracks in the rock, and then expands as the water freezes, exerting pressure on the surrounding rock. Wind can carry sand and other sediments, which over time can wear away the surface of rocks. Plant roots sometimes get into cracks in rocks and pry them apart, resulting in disintegration.
Chemical weathering changes the chemical composition of rocks, often when water interacts with minerals to create various chemical reactions. One of the most common chemical weathering processes is carbonation, where atmospheric carbon dioxide reacts with chemicals in the rock. Carbonation occurs on rocks which contain calcium carbonate, such as limestone and chalk. Acid rain also causes chemical weathering. A number of plants and animals may create chemical weathering through release of acidic compounds. Lichens, algae, and moss all produce various chemical compounds that can react with chemicals in some rocks.
Biological weathering is a type of weathering caused by plants and animals. Plants and animals release acid forming chemicals that cause weathering and also contribute to the breaking down of rocks and landforms. It involves processes like plant roots widening cracks, animals burrowing, and microbes releasing acid.
Sources:
www.buildingconservation.com/articles/rockofages/rockofages.html
www.john-clarke.co.uk/aberdeen_granite.html
www.thamesweb.co.uk/royalty/queenvicstatue.html
https://victorianweb.org/sculpture/boehm/16.html
https://www.stonecontact.com/corrennie-granite/s12314
https://education.nationalgeographic.org/resource/weathering/