TECTONICS
Thanks to its volcanic inheritance you find Rhyolite in mountainous areas. These violent origins have also created areas where the geology is complex and you’re forgiven for being baffled by the array of rock types you encounter even in one valley. North Wales and the Lakes are particularly well endowed with many varieties of Rhyolite. The Caledonian orogeny some 410 million years ago created mountains across Scotland that in their prime rose to at least 4000m. The ripples from this orogeny also created mountains and caused buckling or folding in the Lakes, Wales, Ireland and Scandinavia
RHYOLITE
True Rhyolite comes from intrusive lava flows and has a calmer smoother texture. Tell tale signs that it once stretched and flowed is seen in the flow-banding that looks confusingly like sedimentary layers. The rhyolites born from more violent births are typically more complex, containing a mix of ash, pumice and other volcanic fragments collected along the way. Those comprised mainly of ash are fine grained and referred to as tuffs, whilst those containing larger grains and imbedded lumps of other rock are known as breccias.
TUFFS
FLOW BANDING
RHYOLITES are produced at low temperatures by partial melting of the crust, and most commonly this happens where subduction is causing 'oceanic' crust to descend into the hot interior of the Earth. Because they contain higher than 'normal' amounts of Silicon they are very sticky, and because they are the first products of melting they contain a lot of water (in the form of a dissolved gas) and other volatile matter. The sticky consistency is also a very effective barrier to good crystal formation, so the rock has a translucent or glassy appearance.
Worldwide, Rhyolite is relatively rare. Chemically it contains mostly silica and is an acidic rock, which makes it less plant loving, in other words a bit cleaner than other mountain rock types.
The Rock at GZ is Rhyolitic lava and was carried from North Wales to the midlands by slowly moving ice sheets during the ice age. It was placed here in 1925.
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IN ORDER TO LOG THIS EARTHCACHE
Please answer the following questions based on your observations
1. (now allowed under new earthcache guidelines - Post a picture of yourself at GZ but not a spoiler and you do not have to show your face if you are camera shy.
2. Describe the texture of the rock and using the listing above and do you think there are any 'tuffs' on the boulder. Describe the impurities you can see, texture and colour.
3. Do you think the indentation markings on the rock are natural or do you think they could be man made? Please explain your reasons.
4. Can you see any evidence of flow banding on the rock? If yes please describe it and give the dimensions. If NOT why do you think there is no flow banding present, please explain why.
5. Is there any algae or moss on the rock and if not why?
6. Please add a NON SPOILER picture at GZ, (Faces are not necessary) as proof of visiting.
This is meant to be easy so please have a go!.