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Tuff but not tough....easy

A cache by wandelaar1 Send Message to Owner Message this owner
Hidden : 04/23/2009
1 out of 5
1 out of 5

Size: Size:   other (other)

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Geocache Description:

To reach this EarthCache could not be easier. It is a viewing point along a paved footpath which follows the coastline for several miles. Very easy access also for wheel chairs.

Lanzarote and the other Canary Islands were shaped from the seabed when millions of years ago underwater volcanoes erupted and land grew out of the sea.
Active volcanoes pour out lava, which is the basis for basalt amongst other types of volcanic rock; they blast out ash and larger material like small and large rocks called bombs as well as blow out gasses and sometimes steam. Lava usually flows down the slope of the volcano but where it has found its way through a vertical fissure or crack in the earth it is referred to as a dike. Where the lava has been squeezed between two other layers of rock horizontally it is called a sill.
When volcanic ash is compacted and has been subject to the elements it becomes a stone like material called tuff. Around the world, tuff comes in many colours ranging from black to brown, red to pink and cream, yellow and green.
The Lanzarote landscape has had millions of years to weather and mature and it is interesting to compare the most recent lava flows which covered part of the island some 300 years ago with the rest of the land. It puts the erosion process and time line into perspective!

You can see evidence of both basalt and tuff all over the island but I have chosen this area near Punta Del Aguila to also cover a specific phenomenon which has fascinated me ever since I stumbled across it. (With thanks to Volker Betz and When in Playa Blanca or Las Coloradas you will notice that the abundant basalt rock has small cavities which are often lined with a white deposit which looks like salt. Usually this is not salt; instead, these deposits are often weathered remnants of zeolites.

NATURAL ZEOLITES BELONG TO A GROUP OF MINERALS WHICH FORM IN THE CAVITIES OR VESICLES WHICH ARE CEATED BY GAS BUBBLES IN THE BASALT.("vesicle" in dictionaryGeology: " a small, usually spherical cavity in a rock or mineral, formed by expansion of a gas or vapour before the enclosing body solidified")This basalt is called vesicular basalt. When this basalt comes into contact with water and tuff, zeolites can be formed in the cavities of the vesicular basalt. The basalt is then called Amygdaloidal basalt.
The term "zeolite" was created by the Swedish nobleman and mineralogist Axel Fredrick Cronstedt (1722-1756). The word combines the Greek "zeon" meaning to boil and "lithos" meaning stone. During chemical analysis the minerals expelled water when heated and seemed to boil and puff up when heated in molten borax, therefore; "boiling stones".

You might think that all of this is quite interesting but unless you are familiar with zeolites, looking at what appears to be no more than sea salt in a hole in the rock is, I suppose, quite boring. Therefore before we go any further to explain the properties and uses of zeolites I suggest you have a look at these websites and I am sure that you will be amazed:
(visit link)
(visit link) (for this site click on each of the mineral names to see a photo)

Zeolites, tuff, basalt, water and heat go together. Zeolites are formed by the crystallisation of substances which have been transferred into the cavities of basalt by water from the surrounding area in a hydrothermal process. This process can take years, even millions of years under varying conditions and temperatures. Natural zeolites can be found all over the world and over 150 have been identified.
Other than being beautiful mineral structures and of particular interest to collectors because of their many different magnificent crystalline forms, zeolites also have very special properties which set them apart. They are micro porous and are made up of a negatively charged structure of aluminum, silicon and oxygen. This framework allows for cations, also called positive ions or for the larger molecules to attach themselves to the negative structure and to be absorbed. Examples of cations and molecules which could reside within the structure are: sodium, potassium, calcium and water. What is special is that given certain conditions such as heat these cations can move in and out of the structure without altering the basic structure of the zeolite and that's why they are often referred to as "chemical sieves". Because of these properties zeolites are mined as well as produced synthetically in large quantities and are used in industry in a variety of applications such as in water softeners, in the petrochemical process when producing fuel, in the cement industry to add special properties to concrete and in cat litter to absorb odour etc.
The location that I have chosen for this earth cache combines examples of basalt, tuff, zeolites and not to forget dikes and sills.
Looking towards the Castillo de las Coloradas you can see examples of all, be it that to experience the beauty of zeolites you may need to go to a web site or a museum. Leave no trace!

To qualify for this EarthCache you have to answer the following questions correctly:

1) Looking towards the Castillo, what is the colour of the tuff to the right of the cache?
2) Is the wall of this tuff formation a) vertical b) concave c) convex?
3) Estimate the average diameter of the vesicles in the basalt rocks on the viewing platform around you.

Please send the answers to tasks 1, 2 and 3 per email via my profile and wait for the ok before logging your entry.

If you like to add a photo of the beautiful surroundings I would be very happy to share your experience



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