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Stalactites?
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John S. White
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PostPosted: Apr 28, 2008 04:23    Post subject: Stalactites?  

Here is another topic for the Forum, triggered by the new set of photos from Tracy of "stalactites" from her collection:

http://www.fabreminerals.com/forum/Message-Board/viewtopic.php?p=1307#1307

I have a bit of a problem with calling these elongated crystal groupings stalactites, which I do not believe most, if not all, of these are. The term stalactite has a rather specific meaning, and it goes something like this: "Icicle-like growths of a carbonate mineral (usually) formed by water dripping from the ceiling of a cave or cavern." Most are usually calcite but the rhodochrosites from Argentina are a notable exception. The term stalactite is specific in that it refers to those formations that hang down, as opposed to stalagmites which grow up from the floor from the same drippings. In the case of Tracy's specimens, they could just as well be stalagmites as stalactites, but I do not believe they are either. I realize that Marty Zinn used to call all such elongated growths "stalactites" but I am sure that was just a term of convenience so that he didn't have to describe every time what it was that he was then specializing in. Note that the vast majority of true stalactites are not covered by visibly distinct crystals.

Perhaps we can come up with a new term for such formations, in which case I feel we would be doing the hobby a favor.

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PostPosted: Apr 28, 2008 09:19    Post subject: Re: Stalactites?  

Hi John -

You raise a really interesting question, and one which I was actually musing over last night while posting my photos. It went through my head that maybe these weren't stalactites at all, because I couldn't imagine the pyro crystals forming out of dripping solutions, and the quartzes visually suggested upward growth rather than downward. Of the 3, the one which looks most like a stalactite to me is the pyrite, however it doesn't meet your definition of a stalactite. Nevertheless I went by the label and information communicated to me.

I will revisit the "stalactites" in my collection and question almost all of them I'm sure. In the meantime, I propose changing my theme of last evening from "stalactites" to "elongated crystal formations which are not contacted except at one end." Would love to hear more comments on your proposal to find a new name for these things - would be worthy of a new topic in my opinion.

Thanks for clarifying -
Tracy

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PostPosted: Apr 29, 2008 08:12    Post subject: Re: Stalactites?  

Opal "stalactite" (actually, I think, a stalagmite) from cave in hornfels, Huanuni, Bolivia. Formed by sulphuric acid acting on silicates, rather than the more usual carbonic acid on carbonates.

This specimen went from me to Marty Zinn to Rob Lavinski to... ?



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PostPosted: Apr 29, 2008 09:17    Post subject: Re: Stalactites?  

The "stalactiites" pictures and discussion have been interesting (I've been busy, just catching up on viewing them all now).

One can sometimes perhaps get away with calling some of these mineral formations "stalactitic", which can imply stalactite-like shape without necessarily really have grown quite that way. "Stalactoid" would be even better, but I've never heard anyone say that. Or one can just keep saying "stalactite-like" and leave it at that.

Malachite, of course, is another mineral that commonly forms very stalactite-like (or, stalagmite-like) growth.

Alfredo, your opal "stalactite" is reallly something. Are you sure it isn't a petrified one of those new compact fluorescent lights? You might try plugging it in and see what happens.

And Tracy, off this topic, but that was a particularly nice dioptase cluster... reminded me of one of those artificial clusters from a crystal-growing kit! : )

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PostPosted: Apr 29, 2008 11:32    Post subject: Re: Stalactites?  

Off this topic, thanks Pete! It has a wonderful NATURAL glow.

Just for fun: hastily taken (indoor/outdoor) photos of a calcite helectite from Bisbee, 10 x 8 x 6 cm, with points of attachment at both ends. Would love to know how these formed - am guessing it's in a manner similar to stalactites and stalagmites, but I can see distinct crystals throughout. Would helectites qualify as stalactite-like formations?



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PostPosted: Apr 29, 2008 11:50    Post subject: Re: Stalactites?  

Stalactoids, I love it. Tracy, someday when you are out in Arizona you will have to come by and see our collection. We have a number of Arizona stalactoids you might like to see, especially the crystallized helictites that have been collected out of some of the mines in Bisbee.
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PostPosted: Apr 29, 2008 12:16    Post subject: Re: Stalactites?  

I should wait and let others comment on your question, Tracy, and of course likely they will (John?), but I'll shoot out a reply too.

Probably depends on how closely one requires "stalactite-like" to be truly "stalactite-like". In fact, a helictite (the correct spelling) is itself not quite a stalactite, just related, one might call it "stalactite-like"; they are both "speleothems", the general name for all cave formations. Well, thinking about it, perhaps helictites are considered to be a type of stalactite.

Helictites are generally defined as mineral growth formations in caves that are not controlled by gravity, but grow in irregular directions, determined by the orientation of crystals at the tip of the formation. Usually in caves, they are of aragonite, and they are fed by water moving through a small central channel within the helictite. I'd never really thought about whether those irregular Bisbee calcite growths would be considered helictites or not; is that what people commonly call them?

I've always loved those Bisbee calcite formations such as you showed, especially the curved, scaly-looking ones that look for all the world like shrimp (minus the legs and all, ready to be eaten as shrimp cocktail).

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PostPosted: Apr 29, 2008 13:02    Post subject: Re: Stalactites?  

...from the root word helix, I assume - makes a lot of sense. Thanks for the spell check!
Here's another one I have, 8 x 6 x 3.5 cm. The crystals aren't as large, but the form is fun - nicknamed "the dog."

Les, would love to see your stalactoids. No plans to come to AZ any time soon, but if things change I'll let you know. Thanks! :-)



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PostPosted: Apr 29, 2008 13:15    Post subject: Re: Stalactites?  

There you go Alfredo, muddying the waters!

Pete
I see nothing wrong with stalactite-like or stalactitic as long as it is used in a discriptive sense and not a generic one. But stalactoids just doesn't roll off the tongue, and shouldn't it be stalactitoids, which is even worse?

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PostPosted: Apr 29, 2008 13:22    Post subject: Re: Stalactites?  

"The Dog" is just incredible! Surely it's glued together and constructed, Tracy. Needs to be labeled "not only repaired, but creatively enhanced"!
(just kidding, just kidding)
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PostPosted: Apr 29, 2008 14:03    Post subject: Re: Stalactites?  

John, one could argue that "stalactite" doesn't roll off the tongue any better than "stalactoid" does...
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PostPosted: Apr 29, 2008 14:15    Post subject: Re: Stalactites?  

Tracy, thank you. I am still trying to figure out where John came up with "stalactitoid" since we did not start with "stalactitite".
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PostPosted: Apr 29, 2008 14:28    Post subject: Re: Stalactites?  

This is gettin' pretty complicated. Maybe if the original word had been stalactitite, the "oid" version would become stalactitititoid.

But what this reminds me of, is one year way way back, over the P.A. system at the Tucson Show, announcing one of our meetings, the announcer broadcast the meeting or lecture of the (enunciating the 6 syllables quite clearly) "FRIENDS OF MINERALOLOGY". Anybody else remember that? (quite likely, it still happens)
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PostPosted: Apr 29, 2008 15:47    Post subject: Re: Stalactites?  

Thanks all for brightening my afternoon!

- Seriously though, what's a recommended way to label my stalactites-that-aren't-really-stalactites?" Personally I think "stalactoid" could be a useful term, if I (and/or other hobbyists) don't know for certain whether it is stalactite or stalagmite or just an elongated growth formation (and might even encompass helictites)...

Hmm, but then thinking a bit further, would dendritic specimens qualify as "stalactoid?"

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PostPosted: Apr 29, 2008 17:19    Post subject: Re: Stalactites?  

Dendrites are a completely different animal. Besides, I don't see your pyromorphite or pyrite as stalactites anyway. Why call them anything other than the mineral they are?
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PostPosted: Apr 29, 2008 19:16    Post subject: Re: Stalactites?  

Points taken. So I will amend my labels to read:

Quartz - stalactite-like (or stalactoid orstalactitic) formations
Pyrite - [I don't know how to describe the specimen so will leave it blank for now]
Pyromorphite - columnar arrangement of crystals

In truth I had my own doubts as to whether the pyro really was a stalactite, so it wasn't unexpected that the collective opinion doesn't think so.

Still hope to see Les' stalactoid AZ specimens someday. Thanks much!

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PostPosted: Jul 08, 2018 16:00    Post subject: Re: Stalactites?  

Reviving this once popular theme thanks to a recent acquisition from the Kay Robertson collection...she named it "Horn of the Dilemma" for understandable reasons!!!

This remarkable...and puzzling... helictite comes from the Ojuela Mine and shows an extremely well developed Archimedes-screw morphology tapering to a point. It's also somewhat reminiscent of the growth patterns of a narwhal's spike (really an elongated tooth), but I can find no sign that there is anything organic about its origin.

The regularity of the spiral and the tapering to a point suggests a persistent systematic spiral dislocation or systematic poisoning of the growth. (Probably worth noting that the point might actually be the start of growth rather than the end, so discussions of sense of spiraling are a bit fraught?)

At first I suspected it crystallized originally as aragonite like most speleothems, but later inverted to calcite. But looking closer, the oveall coils of the screw look like they are in turn made up of smaller twisted coils like a twisted rope made up of smaller twisted threads. Under the scope it appears these threads are composed of flattened rhombohedra with their c-axes oriented perpendicular to the length of coil...so that what you see as the texture of these threads is the zig-zagging of the edges in the plane of the a-axes (this indicates growth as calcite, not aragonite) It gets wierder yet, the small scale coils appear to be coiled in the opposite sense of the major coils!! I think this may only be apparent, reflecting the fact that the trailing edge of each stacked rhombohedron points "up" and as they wind around to the "left" this creates an apparent right spiral.


I have another specimen that might shed some light here and will post pictures of it forthwith



20180708_120857.jpg
 Mineral: Calcite
 Locality:
Ojuela Mine, Mapimí, Municipio Mapimí, Durango, Mexico
 Dimensions: 75 x 55mm
 Description:
Peter Megaw specimen (ex Kay Robertson) and photo
 Viewed:  974 Time(s)

20180708_120857.jpg



20180708_121006.jpg
 Mineral: Calcite
 Locality:
Ojuela Mine, Mapimí, Municipio Mapimí, Durango, Mexico
 Dimensions: 75 x 55 cm
 Description:
Peter Megaw specimen (ex Kay Robertson) and photo
 Viewed:  974 Time(s)

20180708_121006.jpg



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PostPosted: Jul 08, 2018 16:14    Post subject: Re: Stalactites?  

So, here's another possible member of the same spiral growth family. This stalactite is siderite and shows two very distinctive growth patterns. One is very straight and linear stemming from stacking of a series of individual rhombohedra with coincident c axes. The other shows a coiling pattern, again composed of individual rhombohedra linked along their c-axes, but with a slight spiral dislocation between each one...creating the spiral. To a lesser degree than in the Ojuela piece the patterns of the individual rhombs create a counter-spiral to the overall "left-handed" spiral.


The fact that both styles of rhomb-stacking occur on the same specimen suggests that something changed and caused the spiraling to begin after the straight growth stage....chemical or simply physical???



20180708_134529.jpg
 Mineral: Siderite
 Locality:
San Antonio Mine (San Antonio el Grande Mine), East Camp, Santa Eulalia District, Municipio Aquiles Serdán, Chihuahua, Mexico
 Dimensions: 180 x 35mm
 Description:
Peter Megaw specimen and image
 Viewed:  962 Time(s)

20180708_134529.jpg



20180708_134601.jpg
 Mineral: Siderite
 Locality:
San Antonio Mine (San Antonio el Grande Mine), East Camp, Santa Eulalia District, Municipio Aquiles Serdán, Chihuahua, Mexico
 Dimensions: 180 x 35mm
 Description:
Peter Megaw specimen and image
 Viewed:  962 Time(s)

20180708_134601.jpg



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PostPosted: Jul 08, 2018 16:18    Post subject: Re: Stalactites?  

It looks the Ojuela calcite spiral is composed of individual strands twisted like the Santa Eulalia siderite.


Kay named her former specimen very well indeed!

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PostPosted: Jul 08, 2018 16:26    Post subject: Re: Stalactites?  

What about chirality ?
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