FMF - Friends of Minerals Forum, discussion and message board

[Ru Smith]

Here's something I'd not noticed before - epitaxial growth of tiny baryte crystals on witherite, from the Scaleburn Vein, Rampgill Mine, Nenthead, Cumbria.

Does anyone else have examples?

[Jesse Fisher]

Baryte replacing witherite to varying degrees is fairly common from some of the Nenthead area mines.

[Ru Smith]

Have you ever seen epitaxy on any of the Nentsberry Haggs examples, Jesse? Mine all show a randomly orientated scatter of baryte microcrystals, whereas they beautifully line up parallel to the witherite crystal edges in this Rampgill piece.

[Pete Richards]

That's a neat specimen, Ru. Is the epitaxy typical for that mine, common, rare...?

I have not seen that relationship before, though the two classic review papers on epitaxy both mention it, though my notes don't indicate any specific locality.

The papers:

Vultée, Joachim von. 1952. Orientierten Verwachsungen der Mineralien. Fortschritte der Mineralogie 29-30 (for 1950-1951): 297-378.

Mügge, O. 1903. Die regelmässige Verwachsungen von Mineralien verschiedener Art. Neues Jahrbuch fur Mineralogie, Geologie und Palaeontologie, 16th Beilage-Band, 335-475.

[Jesse Fisher]

Ru - I have one witherite from Haggs in the collection, but unfortunately, I see no evidence of Baryte with or on it under the stereoscope.

If you are ever in Weardale, you should look up local collector Helen Wilkinson. She has drawers full of the stuff, all personally collected.

[nurbo]

Hi Ru,
I checked my selection of Witherite's from Haggs and none show this kind of regular structure where the surface has altered to Baryte, The specimens I checked all showed a random ordering of the Baryte's that are large enough for me to see, I wish i had access to a good microscope, id like to be able to check the Baryte where it forms a crust, the individual crystals are way too small for me to see so i don't know how ordered/disordered they are.
The Baryte alteration, to greater and lesser degree's, is present on the majority of Witherite's from Haggs, I was told that the clear Witherite's are "Very unusual" by a very seasoned local collector. I've got some similar Witherite/Baryte pieces from North Yorkshire I'll check those at some point too.

That's a really interesting piece Ru any chance of some more photo's?

[Ru Smith]

Thanks very much for the two references Pete. This is the only example of epitaxy I have seen from Rampgill. mindat shows 6 witherite photos from there, none with epitaxial overgrowths.

Thanks for the tip, Jesse.

I'll take some more photos when the weekend arrives, nurbo.

[Ru Smith]

Allright, weekend is here. A few more witherite photos. Firstly another view of the Rampgill specimen, then a few other Alston Moor specimens, none of which shows the epitaxial overgrowths, and finally a Yorkshire example with randomly orientated microcrystal overgrowths and a hollow interior from which all of the witherite has gone.

[nurbo]

Firstly a Baryte after Witherite from Moulds Top near Arkengarthdale,

Ru, your hollow North Yorkshire piece reminded me about this one I have, its a Baryte cast or maybe an epimorph, after Witherite from the Haggs Mine which is hollow, I guess either the Baryte coated the Witherite and then the Witherite was etched away or the surface of the Witherite was partially pseudomorphed to Baryte and then the Witherite was etched away, inside the hollow part are tiny Quartz and Sphalerite crystals,on both pieces the Baryte shows no discernable pattern.

Great Rampgill piece Ru

[Ru Smith]

Lovely specimens, nurbo. Thanks for showing them!