Introduction
I've been wanting to put together an EarthCache in the Trafford Centre for ages - in fact it turns out I started thinking about it over 18 months ago - but the problem in doing so stems partially from the fact that there's so much to see, and it's difficult to know what to focus on and where to pitch it.
There's also the issue of getting people to relevant indoor locations where GPS doesn't work and without using store name references - because they change from time to time and there's also Groundspeak's commercial guidelines to consider.
After numerous visits and months of cogitation I think I've cracked it though 
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Anybody who knows me knows that shopping is one of my least favourite pastimes but I rather like going to the Trafford Centre as, while for most people its magic is found in the wide range of colourful retail outlets, the magic for me is in the geological history which is laid bare in the impressive and varied rock types which adorn the floors and store fronts .
The Trafford Centre opened in 1998 after just over 2½ years of construction, at a cost of 600 million pounds. Extensive use has been made of natural stone for the floors of the malls and for the frontages and interiors of the shops. The floors of the main malls are made of just seven different stones, comprising two granites, three gneisses, a marble and a serpentinite. The slabs are 2cm thick.
Logging Tasks
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PLEASE REMEMBER this EarthCache is on private property with the full knowledge and permission of the property owner so you can feel completely free, if challenged, to explain the full details of the activity you are undertaking so that any and all interested parties can be confident your activities align fully with the safety and security requirements appropriate to a venue of this type. This is one geocache where 'Stealthiness' is absolutely not required.
- What colour is the oldest rock?
- What colour are the two rocks which include phenocrysts?
- What colour is the rock that was formed at the greatest depth?
- What colour are the two rocks which are the opposite of HORRID?
- Only one of the rocks here might contain fossils of sea creatures - what colour is it?
- Of the two rocks which include phenocrysts, please tell me the size of the largest phenocryst in each rock type and, on that basis, which of those rocks cooled from its molten state to form solid rock the quickest of the two.
- What lies under the circular brass plate in the ground floor near the elevator?
- Optional task: feel free to add any photographs of your visit that do not show the specific features from the logging tasks - no spoilers please. In the interests of allowing everyone to experience the EarthCache fully for themselves obvious spoiler photographs will be deleted.
Background
On planet Earth there are three main types of rock:
- Sedimentary
- Igneous
- Metamorphic
This EarthCache shows you examples of all three types on a grand scale and, as all the stone has been polished, provides an opportunity to get a really good look at the internal structure of each type.
Igneous rocks are formed by the cooling of magma (molten rock) deep within the Earth or at the surface. Sedimentary rocks are formed from fragments of other rocks which get cemented together by minerals. Metamorphic rocks start off as one type of rock and are changed into a different type of rock by extremes of heat and/or pressure.
Make your way to the bottom of the escalators on the ground floor under the main dome at the intersection of Peel Avenue and Regent Crescent and get ready to study some fine rocks 
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BLUE Rocks
Standing at the bottom of the escalators you'll notice that the rocks in this section of floor are arranged in a circular design which mirrors the shape of the circular dome above you.
The centrepiece of the design is made up of two rare BLUE rocks - one DARK BLUE and one LIGHT BLUE.
The DARK BLUE rock is a type of granite from Brazil, an intrusive IGNEOUS rock. Igneous rocks are sometimes called fire rocks because they are formed when very hot molten rock cools. INTRUSIVE igneous rocks form deep down in the Earth and EXTRUSIVE igenous rocks form when molten rock cools on the Earth's surface.
This medium grained DARK BLUE granite was formed around 700 Mya (million years ago). Crystals of sodalite give the rock its blue colour and these are interspersed with crystals of black biotite. Notice how the arrangement of crystals is fairly random with no obvious direction or pattern.
The PALE BLUE rock, also from Brazil, was at one time a SEDIMENTARY rock - a sandstone made almost entirely from sand grains of pure quartz but massive heat and pressure caused the sandstone to metamorphose into the rock you see here today - quartzite. This pale blue quartzite is a METAMORPHIC rock and is probably the oldest rock found here at around 1.2 billion years old!
Notice the distinct bands of colour in the quartzite and the way some layers cut across other layers - a relic of its earlier sedimentary state. This quartzite gets its blue colouration from a mineral called dumortierite.
RED Rock
Working outwards from the blue rocks at the centre of the circle the next rock we find is another granite - this time a very coarse grained granite with a robust RED colour brought here from Ukraine. This rock was formed during the Upper Carboniferous period around 300 Mya.
Granite is a crystaline rock - you can see the individual crystals in its structure. The largest crystals in this granite are the dominant RED coloured ones which are made of the mineral feldspar and, as they are much larger than surrounding crystals, they are large enough to be called phenocrysts. The crystals which surround the phenocrysts of feldspar are mainly the minerals quartz (white/clear) and biotite (black).
The large RED crystals took a very, very, very, very long time to grow which tells us that the magma which became this rock spent a very, very, very, very long time cooling underground 
. If the magma had cooled more quickly i.e. at the surface the crystals wouldn't have had long to grow and would have been much smaller.
In fact, the presence of both very large and much smaller crystals in the same rock probably indicates multiple periods of cooling which varied between very long and comparatively short. Different minerals crystalise at different temperatures so here the feldspar has crystalised very slowly and the quartz and biotite have crystalised later and more quickly, possibly as a result of the magma being forced upwards under pressure.
Notice how the crystals in this granite too are arranged randomly, with no obvious pattern or direction.
GREEN and GREY Rocks
Continuing outward from the centre of the circle toward the perimeter we encounter sections of a GREY rock surrounded by sections of a GREEN rock.
The GREY rock is a GNEISS (pronounced NICE) which is another METAMORPHIC rock and this one is also from Brazil. Gneiss is a foliated metamorphic rock which means that it has obvious, distinct bands of colour which, in this case, are a salt-and-pepper mixture of black and white which make this gneiss look GREY over all.
The Earth’s crust is made up of fifteen or so enormous tectonic plates, which shuffle around on the surface. When two of these plates meet they do so with enormous force, enough to squeeze the rocks where they touch hard enough that they re-crystalise and become a different type of rock - the rocks metamorphose and become metamorphic rocks.
The mineral grains in the gneiss (mainly feldspar and quartz) are large enough to be identified with the naked eye and the roughly parallel bands of colour may be straight or tightly folded.
The GREEN rock is from India and is called serpentinite. It's quite special and differs from all the other rocks found here because it comes from much deeper in the Earth. All the other rocks you see here are from the Earth's crust and so would be found anywhere between 1km and 50km below the surface. The serpentinite though formed in the mantle at a depth of anything up to 60km.
Study the serpentinite close up and you'll see that it includes veins of black and white minerals and also has an almost leathery, grooved surface texture which is revealed by reflected light. It's possible that whoever gave serpentinite its name thought it looked a bit like the skin of a serpent perhaps?
PINK Rock
If you've followed the notes about all the rocks so far, working outwards from the centre of the circular pattern then you might just be able to work out what this PINK stone is...
It's a foliated metamorphic rock, its crystals are large enough to be identified with the naked eye, it has interleaved bands of light and dark coloured minerals, just like a rock type that you've already seen. The only difference is, this example is PINK in colour...
Hopefully you've already managed to work out that this is another example of GNEISS .
WHITE Rock
The last example in this circular design is a WHITE rock, a WHITE marble from Italy.
Marble is a hard crystalline METAMORPHIC form of limestone or dolomite rock and this example, which formed around 200 million years ago, includes feathery, pale grey veins arising from impurities which settled in fractures in the rock as it crystalised.
ORANGE Rock
Stand at the bottom of the escalators, facing the steps and look at the shop frontage to your right and you'll see that it's made of a highly polished and unusually coloured stone - a sort of ORANGE coloured stone with a network of mineral veins formed of calcite.
What's unusual about the colouration of this stone is that it's not, as you might suspect, a marble - it's actually a nodular limestone, which we usually expect to be white in colour. This particular limestone comes from Spain and was laid down in a deep sea during the Jurassic period from a poorly sorted accumulation of shell fragments and mud.
A Mysterious Modern Relic
On the opposite side of the escalators to the shop frontage of orange rock you will find the glass elevator in which you can zip between floors and in the floor just outside that elevator you will find a gleaming brass circular plate. Before heading up to the first floor to look at some more rocks, please make a note of what lies beneath this brass plate 
.
BLACK Rocks on the First Floor - Regent Crescent
On the Regent Crescent side of the upper floor there are two different BLACK rocks. To differentiate the two BLACK rocks we'll call them ALLBLACK and BLACK+ as those are accurate descriptions of them - one being entirely black and one including a subtle second colour.
To find these rocks you will need to locate particular shop units using the numbers clearly visible above their doors. Some units have lost their numbers over time, either through re-modelling or through merging multiple units into one, but the two units which house our target rocks have their numbers intact and they are stationed either side of the entrance corridor to the New Orleans French Quarter of the Trafford Centre. An easy way to locate New Orleans is to look out for the large brass statue of a four-piece jazz band .
The ALLBLACK rock is found as a skirting around the base of unit 137. This rock is a gabbro, a coarse grained plutonic rock of crystaline texture. Plutonic is a word that geologists use to describe a rock which solidified at considerable depth below the Earth's surface so yes - this too is an INTRUSIVE IGNEOUS rock. The minerals in this gabbro are mainly pyroxine and plagioclase feldspar.
The BLACK+ rock is found as a skirting around the unit on the opposite side of the corridor, unit number 145. The BLACK+ rock crystallised around 292-298 Mya and is known as larvikite. Nowadays this rock is quarried in Norway.
The larvikite includes phenocrysts (very large crystals) of the the same feldspar found in the gabbro around the base of unit 137, but the feldspar crystals in the larvikite are arranged differently which causes the light they reflect to take on a coloured sheen which enhances its value as a decorative stone.
This concludes your journey around the Trafford Centre - at least for this Earthcache and I sincerely hope that your newfound knowledge will enhance your future visits here 👍