included in:- |
geological walk, Blease Fell |
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ford, Threlkeld | ||
site name:- | Blease Fell | |
civil parish:- | Threlkeld (formerly Cumberland) | |
county:- | Cumbria | |
locality type:- | geological site | |
locality type:- | river | |
locality type:- | ford | |
locality type:- | waterfall | |
coordinates:- | NY29982699 | |
1Km square:- | NY2926 | |
10Km square:- | NY22 | |
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BPR25.jpg The ford on the path up the Glenderaterra valley. (taken 26.9.2008) BPR27.jpg Chiastolite in the Skiddaw Group mudstone. (taken 26.9.2008) |
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The unnamed stream exposes Skiddaw Group mudstones which have been slightly metamorphosed
by contact with the Skiddaw granite intrusion to the north. One of the indicators
is the presence of chiastolite in the rock. This was low grade metamorphism; raised
temperature, but not pressure - notice that the crystals lie in all directions, not
aligned by pressure. |
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Chiastolite is aluminium silicate, a variety of andalusite. The crystals are flat
plates up to 4cm square, usually with a black spot in the middle. |
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The rock is very broken up, and stained by iron. |
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NB: beware my amateur geological knowledge. |
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JandMN : 389 BXO30.jpg Rock, hand specimen of Skiddaw mudstone, moderately metamorphosed to slate with crystals of chiastolite, from a streambed on Blease Fell, Threlkeld, Cumberland, NY29972698, 12 October 2012. Skiddaw group, mudstone; Ordovician, Llanvirn/Arenig. Chiastolite is a variety of andalusite, aluminium silicate, Al2SiO5. (taken 12.10.2012) |
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BPR28.jpg Chiastolite in the Skiddaw Group mudstone. (taken 26.9.2008) BPQ19.jpg Chiastolite in the Skiddaw Group mudstone. (taken 24.8.2008) BPR26.jpg Waterfall above the ford. (taken 26.9.2008) BXM60.jpg (taken 12.10.2012) |
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