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Identity HelpNaming composite minerals

18th Nov 2017 20:26 UTCReiner Mielke Expert

Is there any standard accepted format in naming crystals that are composed of more than one species? For example a crystal that is part dravite and part elbaite. Would it be a dravite-elbaite crystal? An elbaite-dravite, elbaite/dravite .. or ? Of course in the gem world you have more flexability like ametrine so along that line elbavite (just joking)?

18th Nov 2017 23:04 UTCJolyon Ralph Founder

Tourmaline

18th Nov 2017 23:07 UTCReiner Mielke Expert

Tourmaline? Why would you call it that when you know which species are present?

18th Nov 2017 23:28 UTCDon Saathoff Expert

If I KNEW both species were present, I'd label it dravite-elbaite series. (I miss embolite.....)

Don S.

18th Nov 2017 23:41 UTCReiner Mielke Expert

Hello Don,

Wouldn't the word series be redundant? Also why not elbaite-dravite if elbaite constituted the majority of the crystal? One problem, doesn't the dash imply that you are not sure which species of that series it is? What about the case where you have a zoned crystal of elbaite that has a layer of dravite on it. That is you have identified elbaite and dravite of which there is no doubt.

18th Nov 2017 23:43 UTCJolyon Ralph Founder

> Also why not elbaite-dravite if elbaite constituted the majority of the crystal?

You didn't specify before which had the majority.

For something like a tourmaline I'd probably name things based on composition inside - outwards, or base to termination, eg if the core is dravite and the rim is elbaite, I would call it dravite/elbaite

Jolyon

18th Nov 2017 23:48 UTCReiner Mielke Expert

I just used tourmaline as an example so it could be anything. For example I have some annabergite crystals that have pink tips that are erythrite. So in that case would I be correct to label it annabergite/erythrite?

18th Nov 2017 23:56 UTCReiner Mielke Expert

Hello Jolyon,

Your suggestion is along the lines that I was thinking. However as far as I know that is not an option for naming in Mindat. Should it be?

19th Nov 2017 01:21 UTCDoug Daniels

Mother Nature just wants to drive us mineral collectors crazy. She does that because of how us humans have treated the world. That's my response, and I'm stickin' to it.

19th Nov 2017 02:22 UTCAlfredo Petrov Manager

Don's use of "series" is not necessarily redundant because it clarifies that we are talking about a single phase that is compositionally between elbaite and dravite. Without the word "series", some readers might assume that you mean a crystal with dravite and elbaite zones, ie 2 phases.

19th Nov 2017 02:51 UTCReiner Mielke Expert

Hello Alfredo,

"some readers might assume that you mean a crystal with dravite and elbaite zones" That is exactly what I mean. "we are talking about a single phase that is compositionally between elbaite and dravite." That is not what I am talking about.

19th Nov 2017 03:07 UTCAlfredo Petrov Manager

In that case, Reiner, you are quite correct that "dravite-elbaite series" would be wrong.

For the case you are talking about then, I'd recommend not using a hyphen at all, but rather calling it a "zoned dravite and elbaite crystal". A bit long, but it does at least avoid confusion.

19th Nov 2017 06:35 UTCJoel Dyer

Good points here, Reiner, had been wondering about the correct naming method myself, as so many tourmalines (and of course various other samples) are zoned in various ways and directions.

And thanks to Alfredo for an excellent and actually concise naming solution.

19th Nov 2017 08:35 UTCJolyon Ralph Founder

>Don's use of "series" is not necessarily redundant because it clarifies that we are talking about a single phase that is compositionally between elbaite and dravite

Ah. but if we want to be accurate:

Elbaite 49% Dravite 51% compositionally = dravite

Elbaite 51% Dravite 49% compositionally = elbaite

We do not need to label a specimen as 'dravite-elbaite series' if the composition is known'. It's one or the other

19th Nov 2017 10:05 UTCDavid Von Bargen Manager

" For example I have some annabergite crystals that have pink tips that are erythrite." - not necessarily. Color isn't all that definitive in measuring the Ni/Co ratio. You can still have annabergite that is pink (not the nice deep clear red color of pure erythrite).

19th Nov 2017 11:43 UTCJolyon Ralph Founder

"some readers might assume that you mean a crystal with dravite and elbaite zones" That is exactly what I mean. "we are talking about a single phase that is compositionally between elbaite and dravite." That is not what I am talking about.

How do you define what is a 'single phase of mixed composition' and multiple zones of a certain composition.

If you get down to the atomic level the unit cell can either be elbaite or dravite, it can't be both.

So, at some level or another there is zoning.

19th Nov 2017 12:06 UTCReiner Mielke Expert

That is corrrect Jolyon, it can't be both that is why I am talking about separate species that make up one crystal . For example a core of elbaite and an outer layer of dravite. Two distinct zones, two distinct species.

19th Nov 2017 12:09 UTCReiner Mielke Expert

Hello David,

It was analyzed. See: https://www.mindat.org/photo-856025.html

19th Nov 2017 12:13 UTCJolyon Ralph Founder

Then I'd call it a dravite crystal with an elbaite overgrowth.

Giving it a name such as dravite-elbaite would just lead to confusion.

19th Nov 2017 12:15 UTCReiner Mielke Expert

Hello Jolyon,

">Don's use of "series" is not necessarily redundant because it clarifies that we are talking about a single phase that is compositionally between elbaite and dravite" That is correct if we are talking about a single phase that is compositionally between elbaite and dravite, but I am not talking about that.

19th Nov 2017 12:16 UTCOlav Revheim Manager

A single crystal may also be composite for other reasons, such as

- Exsolution lamellaes

- Random distribution of molecules close to the midpoint between two or more species

- partly metamorphosed crystals

- Gradual zoning with an inner zone, an outer zone and a zone with random composition

In these cases the relative percentage will not necessarily be known or interesting. I think that quite a few systemaic collectors would be interesting to highlight the content of kirchsteinite on the label of a sample with "exsolution lamellae of kirschsteinite in magnesium-iron olivine"

Olav

19th Nov 2017 12:25 UTCReiner Mielke Expert

Hello Jolyon,

"Then I'd call it a dravite crystal with an elbaite overgrowth." That certainly is a good description but not what I would call a name or a suitable label. What about an intergrowth that is not as well defined, like multiple zones of different shapes or several species in one crystal? It would make more sense to me to use a term such as dravite/elbaite as this would not depend on the geometry of the zones and would not be confused with dravite-elbaite series. It would also fit neatly on a label.

19th Nov 2017 12:53 UTCJolyon Ralph Founder

> That certainly is a good description but not what I would call a name or a suitable label.

The name for the label would be Dravite, Elbaite.

19th Nov 2017 12:54 UTCJolyon Ralph Founder

You have two minerals, two names. Trying to make a frankenstein name for your crystal containing two distinct species isn't helpful.

19th Nov 2017 12:57 UTCFranz Bernhard Expert

Why not just separate it with a comma: elbaite, dravite.

Franz Bernhard

19th Nov 2017 13:49 UTCReiner Mielke Expert

Trouble is Dravite, Elbaite is the same as a specimen in which there are both species but not in one crystal. If I saw such a label I would be looking for two separate minerals. Not sure why you have changed your mind from your earlier suggestion "For something like a tourmaline I'd probably name things based on composition inside - outwards, or base to termination, eg if the core is dravite and the rim is elbaite, I would call it dravite/elbaite"
I thought it was a good one.

19th Nov 2017 14:50 UTCŁukasz Kruszewski Expert

Tourmaline group. Or, if the species are known to form a solid solution in this specific example, dravite-elbaite solid solution

19th Nov 2017 15:00 UTCNelse Miller

I have a related question, though not about tourmalines. I have a specimen from Ardeth Lake, Boise Co., Idaho which the dealer said had been analysed and found to be compositionaly between spessartine and grossular, mostly spessartine. He did not specify the proportions of each component. Is there a standard as to how to label such a specimen? I would be grateful for any suggestions.

19th Nov 2017 15:01 UTCNelse Miller

19th Nov 2017 15:04 UTCNelse Miller

It appears that I received my answer while I was composing my question. Thank you Mr. Kruszewski!

19th Nov 2017 15:11 UTCReiner Mielke Expert

Hello Lukasz,

I am not talking about a solid solution. Please read the thread more carefully.

19th Nov 2017 15:13 UTCUwe Kolitsch Manager

The more information, the better - so I'd use a smaller label font and "Elbaite (core), dravite (rim)."

And if you have analytical data, put them in the (more detaild) electronic description in your database.

19th Nov 2017 15:17 UTCReiner Mielke Expert

One of many reasons I brought this up is how to best label something like this, which is homogeneous under a normal microscope.

This is a photo by Pavel from an earlier thread.

As technology improves more and more of this is becoming apparent and I find the current method of naming things lacking.

19th Nov 2017 15:18 UTCKeith Wood

Cut the crystal into its component pieces, and sleep well knowing you've got it all sorted!

Without specifying what elbaite-dravite means, a hyphenated label only leads to confusion. The point of language is to say what you mean. And if that means a longer, even cumbersome label, so be it. But if it is zoned, something like "dravite over elbaite" is pretty short. If it is not zoned, then it is one or other, and should just be named whichever it is.

19th Nov 2017 17:33 UTCDonald B Peck Expert

Keith, I like your solution. It seems to me, Reiner, that you are trying to apply a (cobbled) name, when a description is more suitable.

19th Nov 2017 18:15 UTCKeith Wood

Thanks, Donald.

Could just call it "Intergrown w,x,y,z and cassiterite." If you are looking for short and true, you won't get much better than that.

These days there is no reason a label has to have all the information on it. If you keep a database or spreadsheet, and use catalog numbers (as you should), they should refer you to the full description, so the label can be simple. It's main purpose is to connect the specimen to the full information, just as the label you place on the specimen is supposed to do.

There have been entire articles written about single specimens. You can't always fit all the information on a label, so don't worry about it. Accept it, pick a cut off point that suits you for what goes on a label and call it good. But everything goes in the database. For instance, I hate having chemical formulas on my labels. It makes the labels ugly, and anyone can look up the formula if they care. That's my pref. Others like them. Pick what you like and stick with that.

20th Nov 2017 17:44 UTCDonald B Peck Expert

Kieth, Amen!

21st Nov 2017 19:25 UTCRalph S Bottrill 🌟 Manager

Some good points made here by Keith, Uwe and others, but a few points still need to be considered when naming some chemically complex minerals like tourmalines.

Generally we should be very cautious in using mineral series; it strictly infers substitution between two end members but in reality it's usually much more complex, with multiple end members. Eg. In tourmalines they usually contain Na, Ca and vacancies in one site, Mg, Fe, Mn, Al, Li, etc in another, OH/F substitution, etc, so most tourmaline compositions should be expressed in terms of multiple end members, depending how finicky you want to be, and rarely just a simple series between two endmembers.

We should be very sceptical about any tourmaline names without good analyses, including the vacancies, F and Li contents.

Some such minerals can be complexly zoned, eg tourmaline, garnet, amphiboles, etc, to the extent that you can have multiple zones within one crystal representing several different species based on their major elements, not just core and rim. Not everything can get a simple, specific name; "tourmaline group" etc is sometimes the best name.

Despite these issues, sometimes you get specimens difficult to categorise without a series name, eg in Mt Bischoff most of the carbonate is around mid-way between siderite and magnesite with only minor other substitutions, so "siderite-magnesite series" works there, unless you do numerous probe analyses of each specimen to prove the dominant species. The resultant specimen can be of little aesthetic value! I suppose if they also get Mn-rich they can be just called calcite-group but that's a bit vague.

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