FMF - Friends of Minerals Forum, discussion and message board

[Tsinidis Tasos]

Hello!
Some of the amethyst crystals that i have found at Kato Nevrokopi basin are showing milky prism and clear purple crystal tips.I was wandering if this is a form of faden crystal or something else is happening.I don't think these are fadens but as my experience on faden quartz is limited your opinion on the matter will be most wellcome.
All amethyst crystals that show this milky line are double terminated.
Which is the mecanism that forms this type of crystals (milky prism and clear crystal tips)
and what is its difference from faden quartz formation?
Very similar to amethyst crystals from Kato Nevrokopi basin are those found at Lake Balkhash in Kazakhstan.

[Carles Curto]

It looks just as a simple zonation of the color, with deeper shades concentrated on terminal faces. The picture didn't shows faden, an inclusion (into the crystal) that looks as a milky fiber or shabby cotton.

[Konstantinos Ch.]

Hello all!

Taso, hello! Faden Quartz are usually more tabular and the inclusion is fiber-like,as Charles mentioned. Your cluster has a wide zone of gas inclusions at the largest part of the prism and inclusions that give the amethystine color concentrated near the terminations. The effect is typical not only for Amethyst, but even for colorless Quartz crystals, showing milky
prisms and clear tips.


Wonderful crystals btw!

Best regards!
-Kostas.

[Premdas]

Hello Tsinidis, I am looking for that kind of double terminated amethyst so I wonder if you know where I can find some? Thank you.

[Tsinidis Tasos]

Hello Premdas!
I am the only source of this type of crystals from that location.
I will sent you a specimen as soon as i will find it.I have nothing left in my collection as they are very much wanted by Greek collectors and i give them away thinking "I will find others soon" but the last few months i found absolutely nothing!
For your information crystals are small (average size 2-3 cm).The crystal in the foto is the biggest of this type ever found (5 cm).
I will sent you a PM when i will find something.
Tasos.

[John S. White]

This type of zoned quartz is quite common and can be found in many places throughout the world. While the milky centers may indeed be due to inclusions of microbubbles, the amethyst color is not due to physical inclusions, per se, but to the presence of iron and perhaps aluminum substituting for silicon. And they do not always have to be doubly terminated. Many of the amethyst crystals in the geodes from Rio Grande do Sul show such color zoning and they almost always are singly terminated. The famous amethysts from Las Vigas, Mexico, are also colored only on the tips. Elsewhere in Mexico one can find the exact reverse wherein the stems are amethyst and the tips are white or colorless. Doubly terminated crystals very similar to that in the photo have been found in excellent specimens from Due West, South Carolina, USA, and elsewhere.

[Jason]

looks like a jackson crossroads crystal too..have dug many that looked like that..especially the DT's with the clear middles and the purple ends..lots like that come from there

[Harjo]

Hi Tasos,

Very often Quartz double enders have a milky zone, as far as I know this occurs when a crystal breaks of the matrix and when enough fluids were still there and the conditions were still right starts growing again from the fracture plain, exactly why this comes with increased gas and/or liquid inclusions I don't know, I'll check Ryckart on that, or.......you can ask Amir, I bet he can tell you right away :-)

Cheers

Harjo

[Premdas]

Hello Tasos, thank you for your kind answer. Yes I will be really happy to receive a PM when you find some new pieces! I find those wonderfull, especially when they got that hourglass design.

Hello John, when you say "the amethyst color is not due to physical inclusions, per se, but to the presence of iron and perhaps aluminum substituting for silicondo", do you mean this is not really an amethyst, but only a quartz with a amethyst color? Does that kind have the properties of amethyst?

Thank you

[Phil Phillips]

All -

(Yia Tasos!)

I'm aware of clear and smokey faden groups, but can't recall seeing an actual amethyst faden grouping. If they do exist, where are they most commonly found?

Phil

[jacquestouret]

Hi Tasos (Good to see that you still have the time to worry about amethyst in to-day's Greece, all my moral support!)
I do not want to look as an old "maitre d'ecole", but the question that you raise (milky quartz at the base, clear, eventually amethyst at the top) is well known by inclusionists. The milky part (caused by myriads of tiny inclusions, typically less than 1 micron in diameter) corresponds to a rapid growth, with many crystallographic defects, at the beginning of the opening of the cavity (highly saturated or oversaturated solutions). For "Faden" (âme in French), you have in addition an opening rate which matches exactly the one of crystal growth. This gives fibers, which serve later as seed for further growth, either as platy crystals or scepters. The clear top corresponds to a slower growth, giving the quartz the time to reach almost perfect crystalline state. In the case of amethyst, you have an addition a change in fluid composition, either through liquid/gas immiscibility or through incoming of fluids from another source (typically meteoric (surface) fluids, mixing with deeper (magmatic or metamorphic) ones. As said by J. White, amethyst requires Fe in its structure, but only in the forme of ferric iron (Fe 3+). Hence these late fluids do not necessarily contain more iron, but they have a higher degree of oxydation. Once the substitution (Si ->Fe) is done, at atomic scale, th "color centers" must be revealed by some radiation (hopefully natural) passing nearby.
Incidentally, these peculiarities of quartz growth (and others) are currently well shown in a temporary exhibition (Notre Terre, ce joyau) at the Museum of the Ecole des Mines Paris (until the end of August) (J. Mullis collection, Val d'Illiez, not amethysts, but beautifll scepters, and a number of exceptional samples from th ecollection A. Giazotto, Idar-Oberstein, etc.). Anybody welcome, I hope that Greece will continue to provide us with nice quartz, from Seriphos or elsewhere!.

[John S. White]

In response to the question from Premdas, amethyst is indeed quartz, it is quartz that is amethyst-colored due to the presence of very small amounts of iron. Citrine is also quartz, it is yellow quartz colored by iron as well, but in a different state of oxidation. These are varietal names for the mineral quartz. Both citrine and amethyst display all of the properties of quartz, only the colors are different. Hope this helps.

[Premdas]

Hello John, thank you, yes I knew that Amethyst is a quartz, I think I didn't understood your previous post, I thought you were saying that one was not a proper amethyst quartz but just a "normal" quartz coloured like amethyst because of the pesence of Iron; but I didn't know that the amaethyst colour is due to Iron so yes, sure, your commentary helped!

See I am quiet sensitive and my approach to minerals is related to their subtle energy; I am not realy knowledgeable about cristal chemistry, and I have a lot to learn on that field!

Thank you.