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There are more than 30 Aberdeens scattered across the world, but there’s only one Granite City. The North East of Scotland’s geological base is granite and Aberdeen IS the Granite City. Granite buildings are everywhere, ranging from the grandest of monuments to the humblest of tenements. The city of Aberdeen, not only known as 'the granite city' but also the Grey City and the Silver City with the Golden Sands is built extensively of silver-grey granite,( which can sparkle like silver because of its high mica content) from quarries within and around the city.
Yet the market cross of Aberdeen, the finest and best preserved of all the seventeenth century market crosses of Scotland, is made of sandstone ! It occupies a site in the Castlegate, on which a market cross has stood since, at least, the days of Robert the Bruce. Aberdeen once had two crosses. One was the 'fish cross' in the east end of the Castlegate, round which the fisher folk displayed their wares until the removal of the fish cross in 1742. The other, situated at the western end of the spacious market place, was known as the 'flesh cross' from the circumstance that the booths of fleshers stood near it for many years in times when flesh meat was allowed to be sold on only certain days of the week.
The present market cross dates from the year 1686, designed and made from sandstone by John Montgomery. It was thoroughly repaired in 1821 and removed to the present site in 1842 . The decorative hexagonal base features six arches with pillars at each corner, animal gargoyles and medallions. Ten of the twelve medallions illustrate Stewart monarchs; namely James I to James V, Mary Queen of Scots, James VI, Charles I and II and James VII, with the remaining two showing the Royal arms and the burgh’s arms.
The work of taking it down at the first rebuilding of 1821 was gone about as carefully as possible, but in spite of that the beautifully floriated Corinthian column which rises from the centre of it unfortunately fell, and was broken in 3 parts. At the same time a singular discovery was made in regard to the Unicorn which surmounts the central column. When the cleaning operations began the whole structure was black with the sooty grime of years, and seemed to be made entirely of sandstone, as had been agreed upon in 1686,but as the cleaning went on the unicorn began to assume whitish tint, and it was then found that it was made of pure white statuary marble. Apart from placing the whole structure on a granite base, and renewing the decayed portions of the fabric with Morayshire freestone.
Rocks can be divided into three main groups, sedimentary, igneous and metamorphic. All three groups are seen here!
Sedimentary rocks are laid down as particles of material such as sand or mud and then hardened by compaction and lithification into sandstones, siltstones, mudstones and limestones. Fossils are often preserved in these rocks.
Igneous rocks crystallise from magma originating deep beneath the Earth’s surface and may be extrusive (i.e. lava flows at the Earth’s surface) or intrusive (emplaced within the Earth’s crust, below the surface).
Metamorphic rocks are sedimentary or igneous rocks that have been altered by changes in temperature and/or pressure. New minerals grow in response to these changes and their composition depends on the composition of the original rock, and the temperatures and pressures that affect it.
At the very top positioned above the parapet on a Corinthian capital is the white marble unicorn with a gilded horn. Marble is a metamorphic rock and when marble is formed with very few impurities it is white in colour and being composed of calcite it has a hardness of 3 on the Mohs scale. (the shaft and unicorn are replacements from the mid 1990’s the originals are on display in the Tolbooth)
The decorative hexagonal base is sandstone, which forms over the course of centuries, as deposits of sand accumulate in rivers, lakes or on the ocean floor, and the sand blends with calcite or quarts and then undergoes compression. After enough time goes by, the pressure pushes all of these elements together to create sandstone. Because not all sand is identical but instead comes in a variety of colors and grain textures, each formation has a unique appearance.
The steps on which the base stands are granite which is formed when magma with silica contant cools beneath the earths surface, solidifying and forming interlocking crystals. The slower the cooling the larger the crystals. Granite comes in a wide variety of colours including reds, browns, and many shades of grey from almost black to nearly all white.
To claim this earthcache, please send the answers to the questions below to us by email - do not post in your online log.Your log may be deleted if this criteria is not met. Educational guidelines for Earthcaches are set by Geocaching.com and GeoSociety.org (Earthcache) and have to be adhered to.
Compare and describe the feel / texture of the sandstone compared to the granite. How do they differ?
Look closely at the sandstone, can you see any individual grains and how big are they ?
Can you see any wear / erosion on the sandstone? What do you think has caused it ?
Comparing the sandstone and granite as building materials, which in your opinion is the better and why ? ( give reasons)
You can see the individual black specks in the granite of the steps, how big are they? Measure/estimate the biggest one, are they all a similar size ?
Looking at the granite, describe the colour of the steps. Now look at the granite cobblestones, can you see any which are a different colour to the steps ? How do you explain the difference ,if any, in the colour ?
While not compulsery it is always nice to see a photo of your visit
(No hints available.)