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Silurian greywackes on the Berwickshire coast Scotland
  
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Forrestblyth




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PostPosted: Nov 16, 2022 09:10    Post subject: Silurian greywackes on the Berwickshire coast Scotland  

In macro the Silurian greywackes are about as interesting as cement! But in pano they are magnificent. From Eyemouth to Siccar point the geology is stunning.

It is no wonder Hutton looked at these formations in the 1700s and challenged that these had to be laid down over millennia rather biblical time frames.

There is plenty of information on the mudstone and greywackes of this area but I have never found what the pinkish crystalline veins are that can often be seen running through the strata I have chipped a few chunks of this crystalline material to try to see what it is. If any one knows please let me know.



20220818_142328.jpg
 Mineral: silurian greywack
 Description:
Berwickshire, Scotland
500cm to 5 meters thick
 Viewed:  14848 Time(s)

20220818_142328.jpg



20220818_141558.jpg
 Mineral: Silurian greywackes
 Description:
Berwickshire, Scotland
500cm to 5 meters thick
 Viewed:  14868 Time(s)

20220818_141558.jpg



20220818_141318.jpg
 Mineral: Silurian greywackes
 Description:
Berwickshire, Scotland
500cm to 5 meters thick
 Viewed:  14834 Time(s)

20220818_141318.jpg



20220818_141207.jpg
 Mineral: Silurian greywackes
 Description:
Berwickshire, Scotland
500cm to 5 meters thick
 Viewed:  14863 Time(s)

20220818_141207.jpg



20220818_141157.jpg
 Mineral: Silurian greywackes
 Description:
Berwickshire, Scotland
500cm to 5 meters thick
 Viewed:  14845 Time(s)

20220818_141157.jpg



20220818_140412.jpg
 Mineral: Unknown vein
 Description:
Berwickshire, Scotland
70cm x 70cmm
 Viewed:  14872 Time(s)

20220818_140412.jpg



20170625_111707.jpg
 Mineral: Silurian greywackes
 Description:
Berwickshire, Scotland
500cm to 5 meters thick
 Viewed:  14844 Time(s)

20170625_111707.jpg


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Kevin Schofield




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PostPosted: Nov 16, 2022 10:32    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

Forrestblyth wrote:
In macro the Silurian greywackes are about as interesting as cement! But in pano they are magnificent. From Eyemouth to Siccar point the geology is stunning.

It is no wonder Hutton looked at these formations in the 1700s and challenged that these had to be laid down over millennia rather biblical time frames.

There is plenty of information on the mudstone and greywackes of this area but I have never found what the pinkish crystalline veins are that can often be seen running through the strata I have chipped a few chunks of this crystalline material to try to see what it is. If any one knows please let me know.


As it is clearly harder-weathering than the greywacke (not a word we hear often these days!) matrix, I'm thinking that it is likely to be quartz, stained pink by a little iron.

Simple hardness test should confirm...

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Forrestblyth




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PostPosted: Nov 16, 2022 13:38    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

Its not as hard as quartz.

I sometimes find it with the odd vein of creamy white calcite ? next to it. i will try to find a photo of it. This might even be the same material in a larger form ?



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 Description:
 Viewed:  14815 Time(s)

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 Description:
 Viewed:  14777 Time(s)

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 Description:
 Viewed:  14761 Time(s)

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Bob Carnein




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PostPosted: Nov 16, 2022 16:32    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

It appears to have rhombohedral cleavage, which suggests calcite. Is the host rock metamorphic?
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Forrestblyth




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PostPosted: Nov 16, 2022 16:48    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

Bob Carnein wrote:
It appears to have rhombohedral cleavage, which suggests calcite. Is the host rock metamorphic?


It is sedimentary but is classed as borderline metamorphic.There are also loads of volcanic rock adjacent. Andesite lava flows around a lot of these formations. Geologically, it's a very diverse area
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Forrestblyth




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PostPosted: Nov 16, 2022 17:08    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

This is some of the interesting Andesite lava flow that push up through the greywackes. You can easily still see the sticky flow folds in the material. I sometimes see a small amount of the vein in this material as well.


20221006_140552.jpg
 Mineral: Andesite
 Description:
St Abbs, Berwickshire
1 meter
 Viewed:  14750 Time(s)

20221006_140552.jpg



20221006_140548.jpg
 Mineral: Andesite
 Description:
St Abbs Berwickshire
1 meter
 Viewed:  14735 Time(s)

20221006_140548.jpg


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Forrestblyth




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PostPosted: Nov 16, 2022 17:26    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

This is some information from a paper on this area. i don't understand a lot of it lol but it may give a hint to the unknown material.

The lavas of St Abb's Head are generally andesitic, but the constituent minerals are so altered that classification is often in doubt. In thin section the feldspars appear, when fresh, to be mainly oligoclase or andesine, and the ferromagnesians, usually altered to iron-ore, may show the crystal form of hornblende or augite. More basic rock, with labradorite and olivine, is quite common. Micas, particularly biotite, are often present and in somerocks are abundant. The rocks are generally microporphyritic, and under the microscope many show well developed flow-structure. The upper and lower parts of the flows are often highly amygdaloidal, the vesicles being filled with silica and/or calcite

By D.C.Greig. From Scottish Borders geology: an excursion guide edited by A.D. McAdam, E.N.K. Clarkson, P. Stone. Edinburgh : Scottish Academic Press (for Edinburgh Geological Society), 1972.
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Bob Carnein




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PostPosted: Nov 16, 2022 19:37    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

I would recommend that you test the pink material. See whether it scratches a copper coin and/or glass; powder a small amount and place it in hot vinegar to see whether it "fizzes". The presence of calcite and quartz in the volcanic amygdules suggests that either may also be present in the fracture-fillings in the metagraywacke.
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James Catmur
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PostPosted: Nov 17, 2022 06:32    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

A bit further north in Fife the veins are Baryte, Calcite and Dolomite. Celestine has been reported but I have never found the locality. They also seem to be associated with the local volcanic activity
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Bob Morgan




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PostPosted: Dec 15, 2022 08:49    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

I know no geology, but was first put of mind that the pink veins might be feldspar, which according to this report is present.
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Forrestblyth




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PostPosted: Dec 19, 2022 12:51    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

Bob Morgan wrote:
I know no geology, but was first put of mind that the pink veins might be feldspar, which according to this report is present.

I think that is a very good prospect. The hardness of about 6 would account for the strong durability seen in the surrounding matrix that has been eroded by sea action. If it was, as I originally guessed calcite I do not think it would stand the erosion. I think calcite is a lot softer.
Also when I looked up feldspar it is noted that it sometimes glows red under UV. My sample glows red.
Thanks for the help
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Matt_Zukowski
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PostPosted: Dec 19, 2022 13:48    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

Calcite also fluoresces red so that is not an good way to distinguish it from feldspar. To rephrase what others have said above: consider cleavage, reaction with acid, and hardness to distinguish the two. Some of your pictures show nice cleavage. Are the angles in the cleavage about 90 degrees or 60 degrees? The former could be feldspar and the latter is likely calcite. A geologist carries dilute (10%) hydrochloric acid (HCl, also called muriatic acid) to test for carbonates like calcite. If you could get some of this you can do a pretty definitive test for calcite (calcite vigorously "fizzes" with HCl, other carbonates fizz less vigorously, feldspar will not fizz unless it is coated with or contains veins of carbonate). As you pointed out, harness is also a distinguishing characteristic between feldspar and calcite - you should do hardness testing with a variety of known materials with a range of harnesses.
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Forrestblyth




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PostPosted: Dec 21, 2022 06:06    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

Matt_Zukowski wrote:
Calcite also fluoresces red so that is not an good way to distinguish it from feldspar. To rephrase what others have said above: consider cleavage, reaction with acid, and hardness to distinguish the two. Some of your pictures show nice cleavage. Are the angles in the cleavage about 90 degrees or 60 degrees? The former could be feldspar and the latter is likely calcite. A geologist carries dilute (10%) hydrochloric acid (HCl, also called muriatic acid) to test for carbonates like calcite. If you could get some of this you can do a pretty definitive test for calcite (calcite vigorously "fizzes" with HCl, other carbonates fizz less vigorously, feldspar will not fizz unless it is coated with or contains veins of carbonate). As you pointed out, harness is also a distinguishing characteristic between feldspar and calcite - you should do hardness testing with a variety of known materials with a range of harnesses.

trying to be a good newbie and do some testing as advised.
Thought I nailed it as calcite as it fized in HCI based patio cleaner
The the wheel fell off my deductive skills on the cleavage test.
Need to find some reference samples to test hardness next.
This I D business is confusing lol



20221221_102242.jpg
 Description:
HCI Test
 Viewed:  13851 Time(s)

20221221_102242.jpg



20221221_103519.jpg
 Description:
Cleavage test
 Viewed:  13855 Time(s)

20221221_103519.jpg


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PostPosted: Dec 21, 2022 06:25    Post subject: Re: Silurian greywackes on the Berwickshire coast Scotland  

A simple search for 'mohs hardness test kit' might provide what you need. Kits vary a lot in what they provide (and cost)
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