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[Josele]

Although it is not obvious prima facie, this sample is a flattened tectonized incomplete dodecahedron. Nine partial faces can be recognized, always forming a 120º angle with adjacent faces when measured on a plane perpendicular to edge. Opposite faces in vertex composed by four faces forms 90º angle.
As seen, crystal has blue and white zones.
Questions are:
Whole crystal is the same specie, in two colors (white haüyne + blue haüyne)?
Could be a combo white haüyne + lazurite?
Somebody have any reference of similar material?
Thanks for your help.

[lluis]

Hi, Josele

I myself have a translucent in colore octahedron of hauyne (Italian sample), so, in colore hauyne for me is not impossible. But your sample looks to me as what is sold as sodalite or lazurite. From Pakistan.

Seller use to analyze samples, although those in particular I have not read "analyzed"

With best wishes

Lluís

[Josele]

Lluis, thanks for your input.
I also was thinking that white zones could be sodalite but after fluorescence checking I dismissed this possibility because Afghan sodalite shines strong orange under UVA, as seen only in the backside of this sample.
Maybe the crystal is composed of haüyne + lazurite + sodalite? I have understood that sodalite group members can be found mixed in solid solution. Perhaps it would not be strange to find them as separate species in the same crystal.
Relating the origin, it is definitely from Ladjuar Medam area, Afghanistan. There are not sodalite group minerals in Pakistan.

[Pete Richards]

[lluis]

Hi, Josele, Pete

Josele, sorry... Sold by a Pakistani seller, from Afghanistan... I mixed nationalities and places... :-(

I have always heard those pieces as lazurite after plagioclase, or sodalite after plagioclase. As I said, the seller of these pieces knows his stuff and many specimens have been analyzed. This, I have not heard,,,,

Fluorecence in this case is due to contaminants or to void in net,
A part could have and the rest, not,.....

Chemistry is like alchemie....
And being chemist, synthesis, I can assure that I have seen some cases that really make me feel that I need to wear a black robe and a high hat.... :-)

Simply, we do not know all about all....and the devil is in details....So :-)

For me, stubborn mule, a sodalite after anything or an anything after sodalite.

With best wishes

Lluís

P.D.: analysis, and problem solved....

[Josele]

Pete, Lluis, thanks for your help, your wise comments are very appreciated.
Searching here and there, I find a similar specimen labeled as anorthite replacing lazurite (by metasomatism), with attached fluorescent pictures which describe the yellowish shines under UVC as phlogopite, a common specie at Ladjuar Medam area.
Anorthite, lazurite, sodalite, calcite, phlogopite, ...
At last, perhaps the only mineral absent is that which came labeled: no haüyne at all?

[Pete Richards]

As Lluis says, more or less, we could always cut the specimen into slices and put them under the microprobe. Then we MIGHT be able to say "This WAS such and such replaced along zones of whatever structural aspect by another mineral so and so."

Not very satisfying when the specimen is now gone! So sometimes we enjoy having a mystery¡

[Josele]

Definitively I prefer to stay in doubt than cut the specimen in slices!

Anorthite hypothesis for the white stuff is in accord with fluorescence observations, since anorthite can have a whitish fluorescence under both long and short wave UV.
If lazurite / anorthite hypothesis is correct, this crystal would be therefore a partial pseudomorph anorthite after lazurite, isn't it?

Lazurite is: Na6Ca2(Al6Si6O24)(SO4,S3,S2,Cl,OH)2
Anorthite is: CaAl2Si2O8
Seems that lazurite must remove Na, SO4, S3, S2, Cl and OH to become anorthite, Does somebody know how it work the chemical process?

Thanks and cheers!

[lluis]

Josele, I am a chemist, not a geologist...so, what I say is what chemistry says. How it could happen, a geologist could far better say than I.

Sodium, Na, is easily replaced by calcium, Ca,. when a piece is in a medium that is rich in calcium.
An effluent rich in calcium. would deposit it and carry sodium.
SO4, S, Cl would be carried away for any alkaline solution
OH, Na, S, SO4 and Cl could be taken out by an acidic solution.

So, maybe just let the piece in a place where acidic conditions are present....

With best wishes

Lluís

P.S.: when I was young, when Tyranosaurus rex was here, more or less, I remember having a piece of lapis lazuli turned white when I let in a solution of clorhidric acid (trying to erase some stains of iron....). So, I still think acidic conditions....

[Josele]

Thank you Lluis. The acidic solution possibility also explains etched calcite, as can be seen in this sample.

[lluis]

A pleasure, Josele!

With best wishes

LLuís

[Josele]

Just to show this comparative fluorescence picture of some sodalite group minerals and related species.

[Don Lum]

Josele,

Wonderful demonstration!!!

Thank you.

Don

[Josele]

A new surprise with this specimen. Recent analysis identifies the white material as Gonnardite. Seems that plagioclase and gonnardite gives a similar EDS spectra, that's why they were confused.

[Josele]

Even more surprises:

[Martin Rich]

Very interesting. A proof that appearances can be deceiving!

Martin