FMF - Friends of Minerals Forum, discussion and message board

[Carles Millan]

[Tobi]

I think this is a proper way to label the specimen in the best possible way without giving the mineral a name that may be wrong. To call a tourmaline just "tourmaline" may be not a detailed info about the variety, but at all it is not wrong (while, according to John, many "schorl" labeled specimens are named wrong). And you mentioned another important point: Many minerals (for example from the garnet family) simply can't be denoted exactly because they are an intermediate between different members of their mineral family.

I must confess that i already do this "inexactness" to some minerals, e.g. the fluorapatites in my collection are not labeled by that accurate name but only as "apatite". I'm labeling more exact in mineral families like quartz, garnet or tourmaline, but i wouldn't mind to have a specimen which is simply described as "tourmaline". At least that would be better than having it labeled "schorl" while it is none.

Cheers!

[John S. White]

In response to Carles' comment I have to say that few crystals of anything are "pure species" and this is especially true for tourmaline group species as well as the garnets. Traditionally they are given the name of the dominant cation or cation pair, even if the dominance of one pair is only very slight. It is impractical to label a garnet 45% pyrope, 30% almandine and 25% spessartine. The convenient name is pyrope. For the most part it is generally safe to label transparent and colored tourmalines from lithium pegmatites elbaite. One cannot go too far wrong, except for the relatively rare occurrence of liddicoatite. My rule, generally, is if the species has been identified and used widely in the literature, then I will assume it is safe to use that name on my labels. If you acquire a garnet from Ft. Wrangell, Alaska, you can be quite certain that it is almandine. A colorful tourmaline from anywhere in New England is almost certainly elbaite.

If such a specimen should end up in another collection, get analysed, and found to be liddicoatite, no one is going to upset with the prior owner for calling it elbaite. There was no attempt to deceive.

[alfredo]

It may be that the apparent abundance of black "schorl" and colored "elbaite" in pegmatites is due merely to: 1) Tradition; and 2) Lack of reliable analyses (which are very difficult and complex to do for tourmalines). In reality some "schorls" are dominantly dravite or elbaite, and some "elbaites" are olenite, rossmanite, fluor-elbaite... and of course tourmalines are notorious for often containing zones of two or three species within a single crystal.

The two most common methods of analysis available to amateurs (powder XRD and microprobe by EDS without standards) are quite useless for identifying tourmalines, so having an "analysis" in one's hand just gives a false sense of security. For all these reasons, I encourage collectors to just use "Tourmaline" on their labels; the viewer can see for themselves whether it's a black one or a pink one.

[Jordi Fabre]

Maybe still better for the labels: "Tourmaline group"?

[Carles Millan]

[Jordi Fabre]

Saying just "Tourmaline" many people would suppose that "Tourmaline" is a mineral species, as Elbaite, Schorl, etcetera, and then we will lose all efforts did to explain the difference between species and groups.

If we label as "Tourmaline group", "Member of the Tourmaline group" or something similar, we could avoid this trouble.

[John S. White]

I am troubled by Alfredo's comment "tourmalines are notorious for often containing zones of two or three species within a single crystal." This implies that tourmaline crystals with multiple zones having compositions different enough to make these zones different species are common. I would dispute that and I challenge Alfredo to support that statement with data. I acknowledge that such zoned tourmalines can exist, but I do not believe that they are common at all. Subtle variations in chemistry are responsible for color zoning in elbaites, but for the most part the crystals are elbaite all the way through.

And if we adopted Jordi's suggestion ("tourmaline group"), then we would have to do the same with garnets, apatites, apophyllites, etc. Bad idea.

[Tobi]

[Carles Millan]

[Tracy]

[Carles Millan]

[Tobi]

No, really not easy. I wouldn't have thought that this topic could lead to such a tricky discussion. First i only saw it from a collector's point of view, but i begin to consider that we should differentiate between different perspectives or rather different types of collections. Let's take the example of a tourmaline specimen which is not yet exactly analyzed:

- If it is in a public collection like a museum, a detailed classification should be done, being followed by an scientifical correct labeling, e.g. "Schorl (Tourmaline group)" or "Elbaite (Tourmaline group), var. Verdelite".

- If it is in a private collection, it is up to the owner, but i personally would prefer the suggestion of simply labeling it "Tourmaline". But an addition with question mark like Carles suggested would be also acceptable for a private collection, e.g. "Tourmaline (Schorl?)".

- If it is offered by a dealer and he has no chance to analyze it, the best could be to label it also just "Tourmaline", or maybe with an annotation in brackets like "Tourmaline (variety not yet classified)".

[Jordi Fabre]

[alfredo]

Jordi, Saying that using just "Tourmaline" is bad because a beginner might be confused about whether it's a species or a group name, is like saying we should not use the word "monkey" when we go to the zoo, because our children might not know whether that refers to one species or a family. I think we worry too much about "confusing the beginners". Give them credit for intelligence. They will learn soon enough, just like you and I did!