FMF - Friends of Minerals Forum, discussion and message board

[nurbo]

Ive been trying to get a decent photo of this for a while, in a vug in the usual Ojuela limonitic matrix there is a tiny stalactite of dark green Conichalcite (or it could be Malachite or even Rosasite I guess, its hard to say without testing) on top of this is a tiny (2mm) hairy spray of lime green Conichalcite,

[nurbo]

Hello,
A killer Witherite, with an interesting tale ... the given locality is under some measure of doubt, it was in a box of Haggs mine pieces but the collector I got it from and myself too think it looks more like a Settlingstones Mine piece, a search on Mindat reveals one piece from Haggs that looks similar from a very reputable UK collector whose localities are beyond doubt whereas it gives several Settlingstones pieces which look identical its certainly from one or the other but Ill leave it as Northern England unless I get proof either way.

[nurbo]

A brief interaction on mindat seems to support the whole Settlingstones theorum, not that anyone seems bothered,. but these things are important, the North of England has ridiculously large deposits of Witherite, mostly massive stuff, much of which was used as Barium ore in Victorian times.

[nurbo]

So I got my Rogerley twin from the Greenbank days YAAAY!. Also a new addition to my collection of twins, Neptunite from the San Benito gem mine.

[John S. White]

Most references describe neptunite as black and, indeed, untwinned crystals from the Benitoite mine are black. But for some reason, and according to John Veevaert, the twins are always heavily included by the mineral crossite so they have the odd color of this one shown by nurbo. Just to complicate matters, crossite was descredited in 1997 as either glaucophane or ferroglaucophane or magnesioriebeckite or riebeckite. Hope that is crystal clear!

[nurbo]

Thanks for that John, I did wonder why the surface structure appears so chaotic it is now, as they say, as clear as mud..
I have another piece which Ive long suspected to be heavily included Neptunite, Ill publish the photo's I have and throw the question open to all observers. I know its almost impossible to be certain without the rock in hand but you never know someone out there might have seen something similar. It took me ages to clean the matrix off this piece, sort of a work in progress, though Ive had it in my collection for about 4 years.

[JohnVeevaert]

I would say this ~could~ be a piece of neptunite that is included. It also has the appearance of heavily included piece of almandine too. The only way to be sure would be ramans or XRD analysis. But then one would ask why spend the $ on a fragment...? I know of only two specimens of twinned neptunite on Miller indices 301 that are not included with amphibole. 99.99% are included and look reddish. These twins are fairly common from the Benitoite Gem mine. Neptunite twinned on 001 is exceedingly rare with less than ten known specimens and they all are free of inclusions.

[nurbo]

Hello ,
Its an interesting piece, it has hundreds of terminal and prism faces on each side, I wouldnt call it a "Fragment" by any stretch of the imagination, my understanding of a "Fragment" is that its a piece broken off a larger sample and doesnt really have any defined crystal structure beyond fracture marks on most sides, this has very clearly defined defined crystal structure on every side, it is more like some kind of insane cluster than a fragment. I just had a poke around on Mindat and Almandine isnt listed from the Dallas Gem Mine so Ive nothing to compare it to. Do you have any photo's of these Almandines John? Id be interested to get a comparison.
Im interested to hear your opinion though,

[nurbo]

Heres a lovely Fluorite I recently got my hands on, unusual green Fluorite from West Pasture Mine.

[JohnVeevaert]

First Almandine was never found at the Benitoite Gem mine. I was merely suggesting that the specimen may be almandine. What I see in your photos looks more like cleavage planes vs crystal faces. And they look a bit hackly which would fit in with almandine. Do you have locality info for this specimen? Neptunite is also harder than garnet so a hardness test might help you ID it. If it is neptunite it is not a crystal but merely a crystal fragment. Try a hardness test on it and report back.

[nurbo]

Hello again,
Outstanding micro crystals of Aragonite from the Heights Quarry.

[nurbo]

Here is a cracking hexagonal Witherite being partially pseudomorphed by Baryte with Quartz and Sphalerite, obviously from the Haggs Mine, which is rapidly becoming a real favourite of mine.

[nurbo]

So I bagged this piece recently in a trade, you can see the mine (with binoculars) from the end of my street. I would strongly suspect the inclusions to be one of the Manganese oxides that are fairly common inclusions in Calcite round here rather than "limonite/haematite" though Ill get some close ups and post them in due course.
https://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=25244

Speaking of which here is a Calcite with what Is regarded as Pyrolusite from the Middlebarrow Quarry in Lancashire. I was going to trim it into three specimens but I think Ill leave it just as it is.

[Philip G]

Hi David,

Yes ... there is a well defined bed of what is generally considered to be a manganese ironstone in Middlebarrow. Although the manganese oxides found within and on the calcites there are as yet untested, they have been given a basic visual identification of pyrolusite. As you know, the same limestone beds are also to be found on the other side of Morecambe Bay and very similar specimens containing manganese oxides can be found at many of the Lindal/Dalton iron mine sites also ... including, probably, the excellent Stank mine calcite you now own and refer to in the John Betts link.

Although Betts did say that it may be limonite or hematite included, with a little bit of local knowledge, I do believe you may well be correct in saying that it is more likely to be a manganese oxide but, of course, without specific testing we cannot say for sure exactly what it is. I have seen calcite specimens from Stank labelled with both pyrolusite and manganite being present ... plus, of course, the well known red inclusions and coatings of hematite.

Cheers.
Phil

[nurbo]

Hi Phil,
Your knowledge of the geology of this area is particularly outstanding, I wondered how far north do the Manganese oxide beds spread without interruption,given that the West Cumberland Iron ore fields end on the beach at Silverdale but stretch out into the atlantic and travel north beyond the reaches of the lake district, I wondered how big the Manganese deposite were, or if they were more just pockets where the concentration of Manganese is significant enough to form crystallisation.

cheers
db