FMF - Friends of Minerals Forum, discussion and message board

[Tracy]

Could someone please provide me with a definition of "floaters" and the processes that give rise to them? I know that they are crystals or groups of crystals that form without any points of attachment, but there seems to be more than one way in which this occurs (e.g., detached from matrix then recrystallized, encapsulated in rock or clay) and I am interested in learning more about the subject. Also, how unusual (rare) is a floater compared to specimens on matrix? Any links to references would be helpful too, my Internet searches have not uncovered anything on this topic as yet.

Thanks,
Tracy

[John S. White]

Now here is a topic that I can relate to and one that should open up a lively dialogue. I have long been a collector of single crystals, which represent one category of floaters. I also collect floater twins which, as the name implies, are two or more crystals related through twinnng but they are unattached to matrix. I agree with you that very little has been written about these, at least not in publications seen in the USA. I did write an editorial touching on the subject that appeared in the Mineralogical Record (v. 25, p. 322, 1994), entitled "Do Your Minerals Talk To You?" Perhaps we can get Jordi to post it on the Forum, it is not very long. Then I wrote about single crystals, or floaters, in my column in Rocks & Minerals (v. 81, Nov/Dec, 2006) entitled, strangely enough, "Single Crystals."

There are fine lines that can be drawn between what precisely fits the various parameters one choses to define floaters. For example, you wrote "without any points of attachment." Well, there are points and then there are points, if you get my point. Some points of attachment are so minute that they are virtually impossible to see without a microscope. I can tell you that most collectors would consider such an attachment to be irrelevant. With respect to the wonderful cubes of pyrite from Spain, one could argue that they were attached to matrix on all sides and, as such, were never floaters. I prefer to consider them floaters. In fact, the vast majority of crystals in single crystal collections are of metamorphic origin and were at one time completely surrounded by matrix, thus totally attached.

So, you have to set your own parameters in deciding what is and what is not a floater, and I hope you will take it from there because, for many reasons, collecting single crystals is a great variation on the hobby. At least you get to fondle them without damaging them and from that you can derive great tactile rewards.

[John S. White]

I also wrote an article entitled "Collecting Single Crystals" and that appeared in Rock & Gem, v. 28, pp. 72-75, 1998

[Pete Modreski]

A related topic, which I believe John has also addressed in one pr more of his past columns in Rocks & Minerals, is the matter of "euhedral crystals" in which, just as with the distinction of what is a "floater", there is a fine line (or perhaps rather, a hazy line) as to how perfect a perfect crystal must be to be considered "euhedral"--totally perfect, or only imperceptively imperfect, or mostly perfect, or perfect as long as you don't look at the side that isn't perfect...

with grins to John,
Pete

[Tracy]

My R&M subscription runs is only a few years old (er, well, only since last year) - please share anything you can! :-)

Thanks -
Tracy

[John S. White]

Perhaps we can get Jordi to post these rather short articles/commentaries on the Forum. The one from Rock & Gem may be too obscure for him to find, but the others will be easy to access.

[Jordi Fabre]

These articles have a copyright and although I can ask permission to publish it here, usually it is a long and complicated process.
How about to write here a kind of short resume of these articles? I think that Tracy don't looks for something elaborated but a simple explanation about floaters.

Jordi

[Tracy]

Yes please, something easy. Your explanation helps me understand how single crystals can be described as floaters, and also why floaters are described as having no discernable point of contact, only the slightest point of contact, or "...with only a small contacted area..." (this is where your point of using one's own definition comes in, right?). What's not so clear is how crystals on matrix, or crystal clusters, can meet the criteria to be called floaters.

Other questions will follow I'm sure. :-)

I'm also a bit puzzled about Pete's likange of floaters to euhedral crystals. Are all floater crystals euhedral? If so, then there seems to be a lot of misuse of the term - and I have some very misshapen "floater" specimens that I purchased under false pretenses.

Thanks.

[Tracy]

Sorry, sent that note out too quickly and left out my most important question: how are they formed??

Thanks again.

[Pete Modreski]

Oh no, Tracy, don't get me wrong, you are quite correct, every "floater" is not necessarily euhedral, but one could argue, that every euhedral crystal must be a floater, because if it had a significant surface of attachment, it couldn'd truly be euhedral.

I was just writing in a very abbreviated way (and attempting perhaps to be slightly humorous, if one knew the background). John White had a column about the common misuse of the term "euhedral", which some people do tend to use to for crystals that are or were totally attached to matrix at their base, or the like. Then they can't by definition be euhedral, which is supposed to mean, completely bounded by well-developed crystal faces.

I was just not taking the time to write any more detailed comments. When people talk about a "floater" crystal, I think it usually has the connotation of being a crystal that formed in an open, hollow cavity or pocket in the host rock, that was presumably filled with (usually hot) mineral-bearing water (hydrothermal fluid) from which the crystals in it grew, but that the crystal has no obvious point of attachment to the matrix. It is, indeed, something of a puzzle to all of us I think, exactly how such "floaters" can form; as John wrote, whether they had some point or points of attachment which are just not obvious, or what.

Crystals that form not within a cavity but within a solid or plastic or soft host rock or material, and are likewise euhedral with no irregularities or imperfections or missing faces to indicate attachment, are recgonized as euhedral crystals, but are probably not generally thought of as "floaters". Here, I would include garnet crystals in metamorphic rocks; orthoclase crystals and bipyramidal beta-quartz crystals that form as phenocrysts in igneous porphyries (where the crystals grew surrounded by molten or semisolid magma); and the perfect pyrite cubes from Spain.

Sincerely, Pete

[Tracy]

I like the notion that perfect crystals which form in soft host rock should be regarded as floaters, just like crystals that formed while suspended in hydrothermal fluids (I imagine that in such cases the specific gravity is high enough that there is enough time for the (re)crystallization process to be completed before the crystal reaches the cavity floor - correct me if I'm wrong here). My knowledge gets fuzzier when I read about specimens described along the lines of:

"Perfectly formed XXXXX crystals completely crystallized on all sides of a YYYY matrix/core. This specimen is a floater, with no obvious points of attachment."

- so was the core fragment of rock floating in suspension while crystals grew all around it? Is the fragment the actual floater, and the crystals secondary growths? I have even seen plate-like specimens described as floaters - did floater crystals form in supension and then sink to the bottom of the cavity to land in roughly the same place? Is this all part of the mystery of how floaters are formed, or just poor use of the floater descriptor?

[Pete Modreski]

I think part mystery, and part poor use of the floater term.

Very few (almost, no) minerals are light enough, or the liquid they are in heavy enough, that they can actually "float" in it, or even sink slowly enough in it for much crystal growth to take place (with or without any matrix fragment around which crystals may be growing).

I guess some have hypothesized that upward flowing currents of solution could keep a crystals or a group of crystals suspended in the water, not allowing it to settle and form a point of attachment, and that is how such "floaters" could form. About the only true examples we can actually observe forming like this in nature, are not crystals, but are "cave pearls" and calcium carbonate oolites in shallow sea floor deposits, where dripping water from stalactites, or wave action, keep the particles agitated enough that they grow concentric layers of calcite or aragonite, with ever becoming attached to the rock or sediment beneath them.

[Les Presmyk]

It sounds like we are zeroing in on defining all crystals in terms of floater (=euhedral), semi-floater (pyrites from Spain) and non-floater (crystals on matrix or a crystal with an obvious point of contact. As a friend of mine is apt to say, "it all depends on whether you are pitching or catching". Is this someone trying to enhance the marketability or value of a specimen? I think the definitions are easier to agree to when someone is not trying to sell or trade another collector a specimen.

To me, if a crystal or crystal cluster is completely crystallized all around, with no visible sign of attachment, it is a floater. Crystals on matrix are not floaters, plates of crystals are not floaters (generally described as such if the back of the matrix or plate has sustained obvious secondary crystallization) and the pyrites from Spain are floaters.

[lluis]

Completely agreed with Les.

Lluís

[Pete Modreski]

Well, I guess I would not exactly agree with what Les says. To me, not just any single euhedral unattached crystal is a "floater". To me, a "floater" is not just a descriptive term, but has shall we say a genetic implication too. I think it implies a crystal of a mineral that normally grows in such a way that you would logically EXPECT it to have some sort of a base or point(s) of attachment, but it doesn't; therefore it at least gives the impression of having "floated" in the solution from which it formed.

People I think tend to use the term "floater" in reference to doubly terminated quartz crystals, minerals in pegmatite pockets (quartz, microcline, topaz, aquamarine, etc.), and the like. I don't think the term is often used for almandine garnets in schist, the Spanish pyrites, gypsum crystals that form in sediments, and that sort of thing.

But maybe I'm wrong, and I'm reading too much into this term. Let's see what others think. (If we're taking votes, I think it's 2-1 against me at this point.)

Pete