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Dolomite variety teruelite

Posted by Erin Delventhal  
Erin Delventhal May 15, 2019 05:29AM
Looking for a little clarification on the dolomite variety teruelite - we list this on mindat as being a variety of black dolomite, yet many examples shown are clearly not black (red, golden, brown, etc.).

Is this term related to the crystal habit seen in these specimens rather than the color?
Alfredo Petrov May 15, 2019 05:52AM
Ha! ...Well, as you know, Erin, no scientific body makes definitions for varietal names, so we're on our own here.

Historically, the name came from the dolomites from Teruel, which have the characteristics of being dark (not necessarily "black", but grey and brown too), euhedral floaters, hosted in evaporitic gypsum and marl.

And then we have a red one, most likely colored by hematite inclusions (common in evaporites) right up there on top of the Mindat page where we call teruelites "black". Is that a teruelite too? Your opinion is as good as mine... The boundaries are fuzzy. (Sort of reminds me of our interminably debated "herkimer" definition... One eventually has to confess that the boundaries are fuzzy.)

Turns out that dolomite as dark brown to black(ish) floaters is quite characteristic of old evaporites, so I'd extend the "teruelite" classification to the dolomites from Chapare, Bolivia, too, as well as perhaps the ones from Hormuz island, Iran, although those have a flatter shape: https://www.mindat.org/photo-162676.html

Have I cleared anything up, or just muddied the waters?
Erin Delventhal May 15, 2019 06:05AM
No, that's about what I suspected, Alfredo.

My reason for asking is that there is also a locality in New Mexico that produces what has, at least locally, been called teruelite. They're very similar to the "honey coloured" examples pictured from Spain. They are also euhedral floaters embedded in gypsum.

It seems to me that the definition we provide for teruelite ought be updated to not be defined by color, but by the geologic context.
I see no reason we can't mention that the original teruelites were black, but the current definition doesn't seem to give much information at all.
Alfredo Petrov May 15, 2019 06:28AM
Then there's the problem of the habit. The original ones from Teruel tend to be simple rhombs. Do we include that as part of the definition too, or do we expand it to include stretched and flattened and twinned habits as well?

Got any photos of your NM ones? I've always had a fondness for that evaporitic environment, underappreciated by many collectors.
Edit: Mindat seems to have just one photo of what we're talking about, from New Mexico: https://www.mindat.org/photo-322715.html

Edited 1 time(s). Last edit at 05/15/2019 06:32AM by Alfredo Petrov.
Erin Delventhal May 15, 2019 07:29AM
It seems to me that the geology is the most important component of the definition, but I did post this with the hopes we could all come to some kind of consensus about it. If anyone has a strong opinion about the habit being a component of the definition, I'd love to hear it.

Here are some more photos of the New Mexican dolomites - I'd like to add these to fill in alongside Dan's image, but I'd also like to have the matter of "teruelite"-or-not sorted out so I don't have to come back and fix them later. ;)

Alfredo Petrov May 15, 2019 07:51AM
I'd opine that those are most definitely teruelites!

We should probably remove the word "black" from the Mindat description; I've never seen one that was truly black. They seem to vary from light brown to dark brown to brownish grey to very dark brownish grey. Whoever wrote "black" was using the word a bit loosely and meant to say "dark".
Erin Delventhal May 15, 2019 08:01AM
We can remove "black," but then we most certainly need to add something back in - otherwise it is a completely undefined variety of dolomite! :P
Erik Vercammen May 15, 2019 08:25AM
I tought teruelite has a special habit: steep rombohedron + pinacoid.
Erin Delventhal May 15, 2019 08:58AM
Erik, is there any source that defines this?
I could probably agree with the steep rhombohedron, but I'd raise some question over the pinacoid. At least per the New Mexican examples I've posted, they fit the steep rhombohedron, but I haven't noticed any with the pinacoid - does that point alone eliminate them from being considered teruelite, even if everything else fits?
Jolyon & Katya Ralph May 15, 2019 08:58AM
The Teurelite that was for sale at the Oxford Show last weekend was absolutely black.

Do NOT remove the word black please :)

Oxford Mineral Show, May 2019
Erin Delventhal May 15, 2019 09:01AM
Jolyon, I have no problem leaving the word black, but the teruelite page either needs to list other colors or to remove the non-black ones.
Jolyon & Katya Ralph May 15, 2019 10:16AM
Trying to research this one a bit more now:

From 'The Mineral Collector (1898)"

Jolyon & Katya Ralph May 15, 2019 10:17AM
Dealers' names are just as good as any - when given right ; but they should always mean something.

I'm just going to leave that here.

Edited 1 time(s). Last edit at 05/15/2019 11:09AM by Jolyon & Katya Ralph.
Jolyon & Katya Ralph May 15, 2019 10:24AM

Every early reference to the name Teurelite refers to the crystals being dark or black, found in gypsum-rich marls.

I think we need to keep the black/dark description, and we should remove the photos of dolomite that doesn't match.

When the name was given it was given for something quite specific. We do no favours to anyone by using the name for similar, but not identical, things.
Erik Vercammen May 15, 2019 11:07AM
Hey's Mineral index says about teruelite: " a black variety of dolomite".
@Elvin: it was something that popped up from the depths of my memory, but I don't remember the source (and I'm even not 100% sure, that's why I wrote "i thought..."

Edited 1 time(s). Last edit at 05/15/2019 11:26AM by Erik Vercammen.
Timothy Greenland May 15, 2019 01:54PM
My Dana gives the reference for Teruelite as "Maestre in the 1845 volume of Anales de Minas p 264". Perhaps someone could consult this and see if the word 'black' is a crucial part of the description. I have no access to the work.


Tony Nikischer May 15, 2019 02:55PM
Mineralogical Magazine, Vol. 12, pg. 393 (1900) is another reference defining the variety as "black". My understanding is the variety was specifically applied to the black, euhedral dolomites from the Teruel Region of Spain. Later, the name "teruelite" came to mean iron-rich dolomite according to DeFourestier. Hence, it appears the varietal name's meaning has changed over time, but if you are a purest, it applies only to those black dolomites from the Teruel area in Aragon, Spain, as originally intended.
Juan Miguel Casanova May 15, 2019 03:24PM
Hola a todos
Como está Alfredo que sabe español escribo en español que me expreso mejor. Con la teruelita pasa algo parecido a los jacintos de compostela. Es una variedad que no está definida. Para mi las terueitas igual que los jacintos de compostela son una variedad de dolomita que aparece en los yesos y dolomías de las facies Keuper que se describió por primera vez en Teruel. Para los jacintos siempre ha estado la controversia del color, para algunos autores son sólo los de color rojo y para otros lo son todos a excepción de los negros. En el caso de las teruelitas no suele existir esta controversia sobre el color e incluso con el tipo de romboedro, lo habitual es el romboedro agudo. Pero sí, son negras, marrones, rojas e incoloras. El color más habitual es el negro.
Juan Miguel Casanova May 15, 2019 03:33PM
Fe-dolomite (teruelite) from the Keuper of the southern sector of the Iberian Mountain Range, Spain. ARRIORTUA, M.; AMIGÓ, J. M.; BESTEIRO, J.; DECLERCQ, J. P. & GERMAIN, G. Acta Geológica Hispánica, 1981, 16,4: 187-188. Estudio sobre la estructura y composición de las teruelitas

Estudio mineralógico de unas "teruelitas" del Keuper de la provincia de Castellón por DRX, SEM/TEM/EDX. ESTEVE, V.; SANFELIU, T.; REVENTÓS, M. M. & AMIGO, J. M. 1993, Boletín de la Sociedad Española de Mineralogía, 16, 1:49-50

Observaciones cristalográficas sobre la teruelita. CHAVES Y PÉREZ DEL PULGAR, F. 1891, Anales de la Sociedad Española de Historia Natural. Actas de la sesión celebrada el 4 de febrero, 20: 9-10

Sobre la estructura de la teruelita. MARTÍN CARDOSO, G. & GARRIDO, J. 1931, Boletín de la Real Sociedad Española de Historia Natural. (Notas y comunicaciones), 3 cuadr., 4 fig., lám. III y IV., 31: 379-398

La Teruelita. FERNÁNDEZ GALIANO, D., 1950, Teruel, 6 (12) 163-174

Hay más bibliografía
Alfredo Petrov May 15, 2019 04:48PM
My point about "black" was that even though the word was used for centuries for this material, it isn't really true. Even the specimen Jolyon depicted above and called "absolutely black" looks dark chocolate brown to me when I look closely. I challenge anyone to show me a truly black teruelite!

And as our Spanish expert Juan Miguel states above, the variety was always considered poorly defined, even by the Spanish, being black, brown, red, and colorless, with black being the most common, and the most common habit being a sharp rhombohedron.

Juan Miguel, many thanks for the references. I have added them to the teruelite page.
Paul Brandes May 15, 2019 06:04PM
I would say leave black in the description, but add that it also is found in a variety of other colours and then list those to avoid confusion.
Erin Delventhal May 15, 2019 07:52PM
Thanks all for the input!
Given Juan Miguel’s description (thanks for that!) and comparison to the situation with the Jacintos del Compostela, it would seem to me that the important component of the definition is the geological context.
The utilitarian part of me would like to argue that the term “teruelite” is much more useful by that definition than by simply being “black dolomite.”
Jolyon & Katya Ralph May 15, 2019 08:18PM
> I would say leave black in the description, but add that it also is found in a variety of other colours and then list those to avoid confusion.

But if the name refers to black/dark crystals (as it certainly seems to do) then that wouldn't be true..

> called "absolutely black" looks dark chocolate brown to me when I look closely

True black doesn't really exist. Everything we call black is a very dark shade of something. But here's not the place to discuss the philosophy of colour but to accept in practical terms they would be described as 'black' by most people.

The term 'Black or dark coloured' works for me. Red crystals, that not the same thing. Light honey brown, not that either.
Ed Clopton May 15, 2019 09:31PM
My "teruelitic" dolomite from New Mexico closely matches Erin's specimens, and the crystals on my one Teruela specimen definitely are reddish-brown rather than black, but I, too, have seen nearly black examples in the past.

With the discovery of similar dolomite crystals in identical environments in other localities since the "teruelite" name became established, it would make sense to define them in terms of the environment and crystal habit, and say that specimens from the "variety locality" of Teruela classically are black or nearly so but that brown, reddish, and honey-colored crystals are well known from Teruela and other localities.
Juan Miguel Casanova May 15, 2019 09:55PM
Jolyon & Katya Ralph May 15, 2019 10:13PM
> With the discovery of similar dolomite crystals in identical environments in other localities since the "teruelite" name became established,
> t would make sense to define them in terms of the environment and crystal habit, }

That's not how names work!

You might as well redefine amethyst to be any crystalline quartz found in volcanic cavities!
Jolyon & Katya Ralph May 15, 2019 10:17PM
I would strongly advise avoiding using the name 'Teruelite' for ANY modern specimens found at localities other than the classic sites for it.

You can compare them to 'Teruelite', you can call them 'Teruelite-like' if you wish (in the description, not the species name). You can of course do whatever you want on your own labels.

Edited 1 time(s). Last edit at 05/15/2019 10:18PM by Jolyon & Katya Ralph.
Erin Delventhal May 15, 2019 11:16PM
Jolyon & Katya Ralph Wrote:

> That's not how names work!

I would argue that this is exactly how names, and languages as a whole, work.
Frank K. Mazdab May 15, 2019 11:40PM
I tend to agree with Jolyon here. In fact, I'd go a few steps further... why can't we just call dolomite dolomite? Is the fact that it's black(ish) and from a evaporitic marl in Spain really so novel that it deserves to have its 1800's-era varietal name promoted into perpetuity? I'd actually never even heard the name before this thread, and I consider myself as something of a mineral enthusiast.
Jolyon & Katya Ralph May 15, 2019 11:52PM
I like these historic names, When used in context, for historic specimens or contemporary specimens from similar localities which could pass for the same thing.

I dislike seeing a name for what is quite an interesting variety of dolomite being diluted by people who have something *slightly* similar but not the same.

The original descriptions were clear on it being black or dark.
Jolyon & Katya Ralph May 15, 2019 11:54PM
ps. just because a crystal came from Terulea and it's dolomite doesn't automatically mean it's Teruleite!
Ralph Bottrill May 16, 2019 12:13AM
This is a bit like arguing if a quartz is amethyst or not, unless you define it with an optical spectographic analysis it’s often subjective and rather pointless.
Erin Delventhal May 16, 2019 02:12AM
Ralph, I don't think we're arguing over simply whether teruelite is black or not, but over whether the usage of that term has evolved over time to encompass something more.
Gregg Little May 16, 2019 05:33AM
It appears that that is exactly Ralph's, Jolyon's and others' point. Once the name encompasses a wide variety of characteristics, far from its original intent, then the name becomes useless. Languages do evolve around popular usage but minerals don't evolve. If a wide range of dolomite colours get lumped into Teruleite then Teruleite might as well be simply called dolomite.

This whole line of thinking takes me back to the earlier nonsensical discussions around "ruby" emerald.
Erin Delventhal May 16, 2019 08:00AM
Gregg, I fully understand that point, but the point I, and others, are trying to make is that we have a choice of two usages:
1) a limited late 1800s-early 1900s name for black dolomite - this is, in my opinion, utterly useless; or
2) a more modern and more encompassing usage of the term to refer to a very specific type of occurrence of dolomite that can result in different colors, but has a distinct geology AND similar crystallography - this is, in my opinion, actually a useful term.
Benjamin Oelkers May 16, 2019 11:15AM
Erin, I would tend to agree that your second option is a more useful term. However, I also very much like what Frank suggested, i.e., just let the term Teruelite be what it currently is: A bit of history that can come in handy when handling old specimen, but not something that one would write on a new label. It seems to me that there is quite some opposition against broadening the meaning of the term, so I personally would not care enough about it to try and convince them otherwise. After all, the time spent to infuse the term with some modern, likely more useful meaning is not going to be worth the effort in comparison to just writing dolomite and possibly some accompanying explanation - at least that is my feeling.
Jolyon & Katya Ralph May 16, 2019 01:20PM
The name is not used enough and important enough to justify this level of debate!
Juan Miguel Casanova May 16, 2019 02:33PM
teruelita is a historical name and in my opinion it should only be used for Spanish localities. Keuper facies dolomite
Donald B Peck May 16, 2019 03:56PM
I tend to agree with Frank. Since the name has a historical place in mineralogy I think we have to recognize the fact without extending it. I just read the Teruelite mindat page and don't have any quarrel with it; but it's content could just as easily be a paragraph on the dolomite page. I have to admit that I have a bias against varietal names, they tend to multiply like mice.
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