EDUCATIONAL LOGGING REQUIREMENTS
In order to substantiate your visit and comply with the educational requirement for Earth Caches you have to submit your answers to the following questions to the cache developers via their profile:
For purposes of logging this cache you must answer the following four questions:
1) Inspect one of the granite toposcopes at the smoke stack. What size are the crystals? What colour are the crystals?
2) What are the three main components of the granite?
3) Go to the information board on the edge of the parking area. What are the four ores mentioned? (Locational question)
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Granites form the backbone of Cornwall stretching from Dartmoor in Devon westwards to the Isles of Scilly. These granites started forming about 300 million years ago when molten rock started to rise into the overlying rock like hot air balloons. When these rising granite balloons reached as far upwards as they could go they started to solidify and form a crystalline mass. This initial crystallisation caused the remaining molten rock to change composition and become increasingly volatile. Every so often the pressure got so much that the volatile mineral rich components escaped through fissures within and beyond the granites.
Kit Hill was formed in these processes and is comprised of granite that originated as molten rock which cooled and solidified deep within the earth's crust. As it cooled, cracks within the granite became infilled by minerals crystallizing from hot fluids. The principal minerals exploited were Cassiterite (tin) and Wolframite (tungsten) and Arsenopyrite (arsenic). Some minor copper and iron exploitation also took place.
The Hill is an archaeological and geological treasure store, having been extensively mined and quarried in medieval times up until 1995.
Kit Hill is a Marylin which is a hill of any height with a drop of 150 meters (492 feet) or more on all sides. The profile of Kit Hill, when observed from a distance, is terraced in nature. This has been brought about in the post-glacial period by freeze thaw and water action leading to a series of slumps in the surface soils.
The Kit Hill granite is a small stock, almost a kilometer in diameter. It is a non-porphyritic biotite granite, containing quartz, biotite and feldspar. The grains are randomly oriented with only small phenocrysts of feldspar, which show little alignment. Non-porphyritic means that the rock does not have a distinct difference in the size of the crystals. Biotite is a name used for a large group of black mica minerals that include annite, phlogopite, siderophyllite, fluorophlogopite, fluorannite, eastonite and many others.
The granite form this hill was extensively quarried as its widely spaced joints enabled the extraction of large blocks. The quarry on the side of the hill (see provided waypoint) will give a good view of the jointing of the granite. The quarry faces show well defined vertical joints at more or less 90 degrees to each other and less well defined horizontal joints. The horizontal joints follow the curve of the land surface. This could have been caused by the contraction of the rock after it solidified and continued to cool and/or decompression as the approximately 3 000m of overlying rock was eroded away.
Kit Hill granite was much used as an engineering stone and was used for docks, bridges and lighthouses in the British Isles. It was even exported
Samples of the granite can be seen in the pillars at the prominent smoke stack on the top of the hill. These have plaques on top showing directions to various towns and features. These are known as toposcopes.
References:
The Cornwall Wildlife Trust
OUGS - South West Branch
University College London
Wikipedia