Strange rough Demantoid

[Ymanda]

Which photo ? I can''t see anything. But i have some rough Demantoid here that look really strange. The owner came back from afganistan with those crystals and some of them show that kind of "snow ball" :

Demantoid 2.38 cts

Even in twins, that snow ball stays in the center of the wole stone, not in eachcrystals that interpenetrate each others:

Demantoid 3.02 cts

3.01 cts

3.51 cts

2.96 cts

5.08 cts

It''s like the more the twin interpenetrate each other, the less that glassy ball is visible. But I could say also that the more the stones are big, the less the snow ball is visible.

In some stones i can see the glassy part has a cystal shape, but in others it is totally round.
Has anybody seen this before? What could be responsible for that ?

And more important, the owner wants US$100 and up for those crystals. Is it too expensive?
I tried to find such stones on internet, but i could not get any Rough Demantoid with ice habbits like those. So i guess it''s quite rare.

 

[valeria101]

Date: 3/2/2005 11:11:4 AM
Author:Ymanda

I tried to find such stones on internet, but i could not get any Rough Demantoid with ice habbits like those. So i guess it''s quite rare.

This is a first for me

Not too long ago Minedirect had "Afgan" demantoid - well formed crystals like that but clear and smaller.

 

[belle]

i''ve never seen anything like it.....very unique. are you thinking of purchasing them?

 

[Ymanda]

Date: 3/2/2005 11:42

0 AM
Author: belle
i''ve never seen anything like it.....very unique. are you thinking of purchasing them?

Not really,

I want to buy only one or 2 of them for my collection and my curiosity. I will try study them with advanced equipment like chemical analysis and spectrometers, but it won''t help me to evaluate the prices. Also for the origin i don''t have much knowledge or trustable datas about demantoids so...
I just know that the owner just came back from a tour in afganistan and Iran with peridots, purple skapolites and those garnets.

Actually, he brought me thoses stones for me to sell them, but i didn''t know what to think about his prices. So I wanted to know more about it because he looks very proud of them and he didn''t want to lower the price.

 

[belle]

very good! any of those would be a great addition to a collection. i hope you will keep us posted on what you decide!

 

[Hest88]

I was just on the phone with Josh of Pala about my demantoid, and asked him about these. He said he''s only seen these types of inclusions (he called them "cottonballs") in spessartites from Namibia, but he''s never seen them in a demantoid. Hopefully that bit of info will help solve a piece of the puzzle for you. Let us know what you find out.

 

[Ymanda]

Ok Thank you Hest88,

So it is a first time on Demantoid to see those "cottonballs"... Cool
Then i can write a small text about that. I knew that Demantoid cristals were rares to find.
That inclusion is then not too bad since it is not found often in Demantoid.

Well i think i''ll accept to take those garnets in deposit...
Thanks a lot

 

[ulysses]

I am newbee on this forum just end up here cause I was searching for some nice garnet crystals,always look around for some nice rare xxx...... so I saw this Demantoid crystals have never seen before ......

...you are sure they are from Afghanistan ?

Where I can get a few of this crystal beauties as well as the purplish Scapolite you were talking about......?

Thanks in advance

Best regards

Ziggy

 

[Ymanda]

Hi Ziggi, welcome, i'm quite new here too..

Well i just posted that thread one hour ago

and i already have some more info about that "coton ball" inclusion (see above). I'm quite sure about they identification just by the color, but i will do a quick chemicall analysis just to check the chromium there. Too bad i can't break one to see the composition of theses "cotton balls".

For the moment you can find more of them on my website, same owner for purple skapolites
And if you are really interested go and check your private message then.
It's 5am in Bangkok, i'm dead i'll just send you my mail and the link to the right page ok ?

See you

 

[Ymanda]

Hi, everybody,

I just wanted to say that i just did the qualitative chemical analysis EDXRF of those garnet. It shows the presence of Silicium, Calcium, Iron (high concentration) and Chromium.

So theses are Demantoid Garnets for sure.

 

[Richard M.]

Hi Ymanda,

I''ve seen red garnets with similar little "cottonballs" in the center. They were abraded alluvial crystals from east Africa, Mozambique as I recall. Sold as "rhodolite," they appeared to actually be some intermediate type of pyrope-spessartite with an orangy cast. I bought a small parcel for faceting, not knowing about the inclusions. They were useless for cutting, of course. I may have some left and I''ll search for them when I go through the long put-off job of organizing my faceting rough one of these days.

When you have a moment, could you please expand on your statement in another thread about techniques for distinguishing volcanic from sedimentary opal? Are there actual chemical/physical/structural differences?


Richard M.

 

[Ymanda]

Thank you for your information about african Garnet.

Yes i can tell you more about opals, with X-ray diffration spectra and Raman spectra. Chemically there is no difference, only the fact that volcanic opals tend to be more porous (H2O is part of the formula)

The main difference is about structure and level of crystallisation:
- Mainly Opales A and C (Amorpheous and Crystobalite-alpha) in sedimentary deposits like Brazil and Australia
- Opals C and CT (Crystobalite-alpha and Tridymite-alpha) in volcanic opals like Mexico and Ethiopia.

C and T are some crystaline forms of sillica.
Spectroscopy Raman and X-ray diffraction are able to separate the differente structures or phasis off the same material (silica).
And it appeared that volcanic opals show some spectra that are very close from those two crystaline forms off silica (C and T), sedimentary opals are more amorpheous.

Both of those origines show some quartz-alpha which present as some micro-inclusions, it''s not part of the opal structure itself.

Sorry for my poor scientific english level, i did my studies in French.

So.. i will make a topic on this with more datas and illustrations, but these are the bases.

 

[Richard M.]

Thanks for the information -- I''ll look forward to more in your new thread. That question bears directly on an informal research project I''m working on at the moment.

Has the mineral moganite (NOT morganite) come up in your work? I''m intrigued by its physical qualities as a "hidden" constituent of chalcedony, and the disagreement by the world''s mineralogical experts as to whether it even exists although they''e named it! I''m attaching an image courtesy of P.J. Heaney from the type locale at Playa del Cura, Gran Canaria.

Richard M.

 

[Ymanda]

What i see here looks like a "tunder egg" or nodule which would be some tuf or tuff (agglomerate volcanic dust). That volcanic dust would regroup and agglomerate due to electrostatic forces and fall on the ground where they are subject to hydrothermal activity with formation of many varieties of the quartz group.

Because the silica can disolve in hot water and then crystalize in different forms which can be mixted in the same matrix or nodule like this one. It is sometime difficult to say exactly what is in there because of the formation of micro inclusions spread in a host micro or pseudo crystaline "crystal" (not mono-crystal) like chalcedony or opal...
For example quartz micro inclusions in Ethiopian opals.

I am not a specialist so, for those who don''t really know about it, please take this as a start for more detailed search for information.

Chalcedony is also found in Ethiopian (volcanic) opals as natural fracture filling.

 

[Richard M.]

No, the moganite is found as crevice fillings, not in lithophysae (thundereggs). I''m very familiar with opal-filled thundereggs, having bruised my knuckles digging them at various locations in the Idaho-Oregon region of the U.S. Some of the most interesting come from Spencer, Idaho where they occur in a perlite formation. They yield very bright and attractive precious opal in thin layers suitable mostly for triplets. But some of the triplets yield cat''s-eyes and asteriated stones that are unique. I have a research paper on them that might interest you.

I''m not terribly fond of Ethiopian opal. I''m a member of the American Opal Society and a great deal of it was offered for sale at our most recent show. The potch color tends toward brown instead of the more attractive red-orange-yellow colors of Mexican opals and it has a bad reputation as being very unstable. But perhaps I haven''t seen the best.

Richard M.

 

[intimategems]

Hiya All!

Just a rundown on the Demantoid....it is actually from Kirman, Iran. Some spell it Kerman. That is where there was the large quake that wiped out half the city. As regards the material, there are several unusual habits that the Demantoid occurs in from the area. It is cool to note that the material is chromium colored and DOES have horsetails in some of the rough. Also....the rough can be a cross between Demantoid and Andradite at times where color banding occurs from the center out. GIA has down a write-up on the material but no one really has done much as regards the crystal aspect. We have some large killer pieces as well as material similar to what is pictures.

Just some notes, from our understanding and experience, the Namibian "Demantoid" doesn't have the horsetails and I don't think it is Chromium colored.

Hope this helps...

BTW: Demantoid also comes from Afghanistan, at least there was a find of it in Khost with the American Military activity there; however, the pocket was small and the material was almost a Peridot Like green color. The material has since been scattered and no more is being produced nor has been for several years. Here is a link to some pics on it at trinityminerals:
http://www.trinityminerals.com/sm2002/june27.shtml

Should you have any questions or comments or need any additional assistance please don't hesitate to contact us!

 

[Sagebrush]

Ymanda,

Beautiful crystals. The price seems pretty good to me though I have never bought demantoid rough. I think the crystals are beautiful as specimens.