Clevedon Shore EarthCache

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Hidden : 8/27/2016
Difficulty:
3 out of 5
Terrain:
2 out of 5

Size: Size: other (other)

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Geocache Description:


This Earthcache explores the mineralised fault on Clevedon Shore.

Clevedon Shore is a 0.38 hectare geological Site of Special Scientific Interest (SSSI) on the beach of Clevedon in North Somerset.

Why is this area particularly interesting? It is because the there is a 'mineralised fault' within the small cliff feature you see here, formed of a rock called Dolomitic Conglomerate.

A conglomerate in geology is a sedimentary rock made up of a conglomerate of much smaller rocks- known as 'clasts', supported in a matrix (ie sand/muds etc). These rounded clasts can range from 2 millimetres to many centimetres in width.

In this case, the sedimentary rock is dolostone, a rock mainly composing of a high percentage of clasts of the mineral dolomite (hence the term dolomitic conglomerate). Clasts enter conglomerates by the processes of consolidation and lithification. The mineralised faulting turned the dolomite stone into dolomitic conglomerate.

Dolomite

Dolostone

Dolomite (calcium magnesium carbonate) is an anhydrous mineral which forms white, grey, pink or tan crystals. The colours and amounts of dolomite and other crystals will determine the colour of the dolostone.

 What is also of particular interest is that the dolomitic conglomerate also contains many tiny clasts (2mm) of other minerals, some of which are very rare and uncommon for the Mendip area- which is why it is referred to as a 'fault'.

 Aside from dolomite, some of the minerals that can be found in the conglomerate cliff are (top left to bottom right):


Pyrite, chalcopyrite, baryte, galena, beudantite, bornite, enargite, sphalerite, hematite.
 Beudantite, in the middle, is generally a rare mineral.

Most of the minerals appear in crystal form on the inside of the conglomerate cliff, however if you look at cracks within the cliff you may see some crystals.- but you'll have to look very closely!

Mineralised faults form in two ways:

1. A very hot steam (of minerals in gas form) forms deep in the earth around a hotspot (an area of increased volcanic activity). The mineral steam rises to the surface and enters rock through cracks. As it cools the minerals deposit and crystallise.

2. A mineral-rich stream ends near to the rock and the stream drains into cracks and joints in the rock. As the water evaporates, the minerals are deposited.

To claim a find on this Earthcache, you must answer the questions below in an email/message to me within 24 hours of logging a find. Any drastically wrong or incomplete answers or any logs from a cacher without sent answers risks their log being deleted. Any photos that reveal answers will also be deleted.

1) Estimate the height of the dolomitic conglomerate cliff you see here (waypointed) and describe some of the colours you see. Try and name some of the minerals that cause these colours.

2) Which of the two explanations above, do you think is most likely to have caused the mineralised fault here? Why do you think this?

3) TO PROVE YOU VISITED: What is the joint surname of the couple on the BENCH waypoint?

Additional non-compulsory extra:

4) Attach a photo of you/your GPS at this location along with any crystals that you see

As part of the 13th International Earthcache Day (October 2015) I challenged myself to place an Earthcache every month until Earthcache day 2016, kicking it off with GC62T8F. This Earthcache is number 11 in that challenge (August 2016).

Additional Hints (No hints available.)



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