Secret Sediments and Cryptic Crystals
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Sometimes, building materials can appear very boring and ordinary. But if you look closer, you can find secrets hidden in the rock. This location, outside the Francis Crick Institute, is a good place to spot a few different types of rock.
While the cache is accessible 24/7, when planning your trip please keep in mind:
- If you are searching for this cache at busy times, please give plenty of space to employees entering or exiting the building.
- If you are searching after dark, please be extra careful with your phone/GPSr as there have been reports of muggings in this area.
Part 1. Secret Sediments
The paving here is Scoutmoor Yorkstone, a type of sandstone quarried in Yorkshire. Yorkstone is commonly used across the UK, because it is very durable and slip-resistant, so is suitable for areas of high footfall. Once you know what you are looking for, you will notice it all over the place. It’s present all over King’s Cross and many other places in London, such as Trafalgar Square. However, there is something unusual about the Yorkstone at the given coordinates, that I haven’t observed elsewhere in London.
Sandstone is a sedimentary rock composed of quartz, feldspar, mica, clay and iron oxides. It’s typically blue-grey to rusty orange with a range of colours in between. Rarely, you can see a purple hue, which is caused by manganese (hint!). Yorkstone is known for having an above average amount of lamination (layers of slightly different sediments), and Liesegang bands of iron oxide.
1. At the given coordinates (on the West side of the crossing), examine the sandstone paving. Then, carefully cross to the East side of the street by the zebra crossing and examine the sandstone outside St Pancras Station (Waypoint 1). Compare the two sets of sandstone in terms of the colours, patterns and degree of lamination (sediment layering) present.
Part 2. Cryptic Crystals
The black stone wall (the one with 'The Francis Crick Institute' written on it) and staircase at the given coordinates is composed of black basalt, specifically olivine-rich ankaramitic basalt. It is commercially known as G684 and is quarried in Northeastern Taimu Mountain, Fujian Province, eastern China. It has erroneously been given the descriptor G which designates granite.
While not as common as the Yorkstone, this type of basalt has been used elsewhere in central London, typically as a paving material. While it appears quite ordinary from a distance, it’s worth a closer look, but since London is hardly the place to be lying down and staring at the pavement this wall is a convenient place to get up close.
Basaltic rocks are the most abundant rock type on Earth. Basalt is an igneous rock, formed from magma rich in magnesium and iron which cooled quickly, producing a relatively fine-grained structure. Basalt commonly contains vesicles, which are small cavities formed from a bubble of gas trapped inside the lava. You may be more familiar with pumice stone, another type of volcanic rock which is extremely rich in vesicles.
G684 basalt contains numerous large round calcic pyroxene phenocrysts, which give the rock a regular spotted appearance, reminiscent of a black jaguar. The matrix surrounding these phenocrysts contains smaller elongated crystals of plagioclase feldspar and tiny glittery crystals of olivine, a magnesium iron silicate. High-quality olivine is also known as the gemstone peridot or chrysolite.
2. Examine the stone closely. Identify the three different crystals described in the paragraph above (calcic pyroxene phenocrysts, plagioclase feldspar and olivine) and report their appearance in the rock in terms of colour, average size and percentage of the total.
3. Does the rock contain any vesicles (small air pocket cavities)?
About the Francis Crick Insititute
The Francis Crick Institute is the largest Biomedical Research Centre in Europe. It was opened in 2016 by Queen Elizabeth II. The institute is a partnership between Cancer Research UK, Imperial College London, King's College London, the Medical Research Council, University College London and the Wellcome Trust. The institute is named after Francis Crick, a British scientist who is most famous for his role in discovering the structure of DNA. Along with his colleagues, he won the Nobel Prize for Physiology and Medicine in 1962.
The Crick offers free exhibitions to promote public engagement with their scientific research. The latest public exhibition is called Cut & Paste. The exhibit is open for drop-in visitors on Wednesdays, Thursdays, Fridays and Saturdays.
Extra information about other rocks you might see in this area (not needed to answer the questions):
White Granite
The basalt steps are capped with a small amount of white granite. Granite is another igneous rock, with a larger grain side than basalt.
Terracotta
The building is covered in terracotta panels; while terracotta is not a natural rock, it is produced by baking clay, a sedimentary rock. The terracotta was chosen in order to appear similar to the British Library, but different enough to give the building its own character. Coincidentally, a large amount of London Clay was excavated to make way for the Francis Crick Institute; the building actually extends half as far underground as it does above ground, due to the need to protect sensitive scientific equipment from the vibrations of the London Underground. (Sadly, the excavated London clay was not used to make the terracotta panels).
Limestone
If you manage to get inside the building as a staff member or guest, you’ll find that the entire ground floor is covered in a very fossily limestone. It has been polished like marble, but is not a true metamorphic rock. In true marble, the original rock forms can’t be recognized anymore, so you would not be able to see any fossils.
Unfortunately, you won't be able to see much of this limestone as a member of the public, so I have included a picture of a fossil below. You can only see a small part of this rock on your left when entering though the visitor entrance. The floor of the public visitor section uses more Yorkstone instead.
