FMF - Friends of Minerals Forum, discussion and message board

[Forrestblyth]

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.

[Kevin Schofield]

[Forrestblyth]

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 ?

[Bob Carnein]

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

[Forrestblyth]

[Forrestblyth]

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.

[Forrestblyth]

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.

[Bob Carnein]

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.

[James Catmur]

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

[Bob Morgan]

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

[Forrestblyth]

[Matt_Zukowski]

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.

[Forrestblyth]

[James Catmur]

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