Big Giant Ralstonite crystal?

I was recently looking at one of my Greenland specimens wondering "why would anyone collect this?" It came in the box with t he rest of the collection and is basically uninteresting massive quartz. That's when I noticed it. A big giant crystal. Or at least the largest one I've seen from Ivigtut. But of what? It looks a lot like that Ralstonite I thought was Wulfenite but it's 7mm long and 4mm wide.

Could this be Ralstonite?

Here are some photos.

Another angle.

And yet another.

It could be a baryte xl too...

If embedded in quartz, it could be topaz. You could easily test the hardness.

Knut

It looks odd and I am not sure what it is. Given the matrix (massive Quartz), I seriously doubt it is Ralstonite. Ralstonite is isometric - octahedra most common, dodecahedra not too rare either - and I do not see any of the faces you show in the pics fit that.

The morphology doesn't really compute with Topaz and Topaz crystals are 'unknown' from Ivigtut (I have seen a few specimens with acicular crystals but never anything major, blocky).

All the best

Claus

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Claus Hedegaard
Google me to find me!

I have seen a remarkable number of ralstonite xls from Cetine di Coturniano Mine (Siena, Tuscany, Italy) and I have never seen this habitus.

Perhaps this is Nabesite then?

It is known to occure at Kvanefjeld plateau, Ilímaussaq massif, Greenland. I don't know about at Ivigtut though. It possible some peices of this collection were from other areas of Greenland.

I originally had reservations about it even being from Greenland, the only similarities with the other specimens being the yellow oxide stains, but then I found a little siderite crystal.

The hardness of the crystal in question though is somewhere around that of quartz. Quartz will just barely scratch it. I can't tell if it will scratch quartz. It appears to be orthorhombic or tetrahedral.

It is for sure NOT Nabesite or other minerals of the Ilimaussaq complex where quartz is nearly totally absent due to the alkaline environment ! A light coloured crystal of feldspar could be embedded in quartz with the observed hardness.

This is going to gnaw at me until I have $30 and a dremel

Jenna, another non-destructive test would be to see if the mineral is fluorescent.

Knut

Hi!
I think that the best proposition so far is feldspar. If the crystal has some broken parts you could look for cleavage/fracture. With a little luck there might be a uninteresting grain of the same mineral on the specimen that you can test.

It doesn't seem to me to be triclinic or monoclinic but I'm not very good with crystal systems and it's a possability. I can't see the entire crystal. Unfortunatly I can find no other examples of it. There are, however, other crystals on the specimen which I cannot identify, but they are poorly formed.

I'll let you all know if I ever figure out what it is. I've been through all the minerals on mindat for the Ivigtut locality and all the minerals that came up on a search for tetrahedral systems and orthorhombic systems with a hardness between 6-7.5 and found nothing similar.



Edited 1 time(s). Last edit at 03/21/2007 09:08PM by Jenna Mast.

Isn'it a flattened quartz crystal? Some cristals have very unusual and misleading forms, as Steno already realised.

Erik:

I've actually been wondering about that. Many of the other crystals on this specimen do appear to be quartz. This crystal seems to have a different luster though. However, it is more similar in color to the matrix than the other crystals, which are clear or yellowish.

For sure .. to me it looks like a small felspar crystal, but I give you, that it will be rare in this habitus, as far as I have seen all feldspars from Ivigtut normally are var. microcline and for sure not transparent ore even semitransparent - they are white-yellowish and more like porcelain in appearence.
Bjarne Ljungdahl
Mineralogical society of Greenland

Bjarne:

The crystal isn't clear but it is translucent such that I can light it up by shining a small light at it. It does not fluorecse under UV (long wave or shortwave) like the other feldspar specimens I have from the region do. It's possible that this was picked up in a slightly different location though. The host rock had some cracks in it, which I broke open to reveal moss like organic material.

Jenna

jenna:

Have you tried contact with Ole V. Petersen or Ole Johnsen in Copenhagen
Geologisk museum ?? or even GEUS copenhagen ??

They are experts in greenlandic minerals.

Bjarne Ljungdahl
Mineralogical Society of Greenland

Bjarne:

I have not contacted them but thankyou for the recommendation. I will try to contact them soon.

Jenna

Bjarne Ljungdahl Wrote:
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>I have had another look at your crystal. Have you tried the hardness ?? I don't think - for sure - that it is from Ivigtut at all..
Bjarne Ljungdahl
Mineralogical Society of Greenland