FMF - Friends of Minerals Forum, discussion and message board

[Les Presmyk]

I once had this discussion with a Ph.D. student in mineralogy and he came from the same point of view as Pete. Actually, his point was that a true floater was impossible because every crystal had to have a point of support. Another argument for another time. I look at a floater as not describing how a crystal formed but what it is from of me, i.e. is the crystal or crystal cluster complete on all sides and is there an apparent point of attachment or damage. If there is matrix, it cannot be a floater.

[John S. White]

I have obtained permission from Wendell Wilson to post my editorial here and from Marie Huizing to post my column here, so this will be done once Jordi returns from his "vacation." I will also try to persuade him to post my column about euhedral crystals, since Pete has introduced that element to the discussion.

As a single crystal collector of many decades, I have to say that in my experience the term floater has always meant a complete crystal or crystal group with no readily discernible point of attachment. This includes garnets from schists and pyrites from Spain that occur in a sort of marl, a soft rock the proper name for which I do not know but I am sure that one of our Spanish contributors will come up with right away. German mineral collectors call them "schwimmers." The term is used in reference to the fact that these crystals show no point of attachment and it has never, in my experience, been used to infer the nature of the crystal's genesis.

Very few crystals appear to have formed while floating in a liquid medium although one could argue that this is the case with phenocrysts of feldspar, for example, in a magma, often seen as perfect euhedrons when the rock which contains them breaks down and releases them as single crystals. I had a micromounter friend who collected what he referred to as "impaled crystals." These were little complete crystals suspended on very fine fibers. He had an amazing array of different species that formed this way and this has led me to believe that this may be the origin of many floaters on a grander scale, where the fibers have been broken away and the points of attachment are effectively invisible because they are so tiny. If one were to limit one's collection to crystals that effectively have no visible point of attachment, even under the microscope, then that would be a very small collection indeed. There are, and have been for some years now, many thousands of quartz crystals from China that appear to be true floaters. I have them from at least three different provinces and I have no idea how they came to be. They do not, in most cases, show any points of attachment. The hematites after magnetite from Argentina appear to be true floaters and I have been told that they are found in a pumice from which they are easily recovered without showing any attachments.

Somewhat common are floater quartzes from the Hot Springs, Arkansas, area which have very atypical shapes. It has been suggested that these are fragments of shattered crystals that have "rehealed," that is, new quartz has grown over the fragment and repaired the broken surface(s). Floaters? I believe they are.

As a single crystal collector I have always used the term floater as more or less synonymous with single crystal, but Les is absolutely correct in stating that you can also have groups or clusters of crystals that are floaters as well. As mentioned earlier I also collect "floater twins" which are two or more crystals in a twin relationship not attached to matrix.

I hope that these comments provide some answers to TAK's questions but she should understand that some of her questions are not anwerable because we weren't around when the vast majority of these crystals grew so we don't know their personal histories.

[str4hler]

I thought I was the only person collecting floaters.... ;-)
damn, I have competition now :-)

Cheers! Frank

[Tracy]

Thanks for your comments John. I wasn't expecting that this would be a question that is easily answered. I had put it to several individuals prior to submitting the posting and none seemed to have a clear-cut answer. If some aspects are unanswerable within our short lifespans, that's information I easily accept.

I cast my modest vote in favor of defining floaters more from the perspective of what they look like than how they came to be - though it seems to me then that clusters which crystallized fully around a rock fragment/core (are these "on matrix?") would thereby fall into this category.

I look forward to reading your articles/columns.

Tracy

[Pete Modreski]

Tracy,

What are some of the locations you have seen, or have specimens from, where the "floater" consists of a piece of rock matrix, with crystal groups grown around it? (And, what are the mineral(s) thereby attached?)

Pete

[Tracy]

I confess I haven't seen or owned any specimens of this type. I do remember coming across a description of something like that in the course of visiting websites, but I am too new to this hobby to have had any details stick with me. I put it out as a hypothetical based on stuff I have come across, but given that I have nothing to back it, it's probably better to cross this one off as a bad example...unless someone else has seen any such things.

[Jordi Fabre]

Waiting to have the chance to publish here the articles, on the meantime I answer this John's request:

....and pyrites from Spain that occur in a sort of marl, a soft rock the proper name for which I do not know but I am sure that one of our Spanish contributors will come up with right away...

The Spanish name fore this soft rock is "marga" and I think that the English translation of this word is: loam.

Jordi

[John S. White]

Sorry, Frank, to break the news but there are other single crystal collectors out there. Oddly enough, there are not all that many, a fact that pleases me because it does reduce the competition. I am reminded of Richard "Dick" Bideaux who collected labels from mineral dealers and collectors. He did not advertise the fact that he collected these because he did not want to invite competition. I feel somewhat the same way about collecting single crystals, but it is such a satisfying aspect of the hobby that I am surprised that more people don't do it.

I also collect quartz and I suspect that there are probably far more quartz collectors than single crystal collectors. This, too, is a very challenging and satsifying specialty because one can always find new and different quartz specimens, often at very reasonable prices.

[str4hler]

Hi John,

thanks for the mental support ; but I was mostly making a joke, like I usually do. Sorry ;-)
I usually don't buy minerals, minerals come to me, so I'm not afraid for a little competition :-)
Examples: In Bologna I stumbled over a 6 cm double terminated Poona-stilibite-xl, on which I cannot find any point of attachment... for 5 euro. Then I stumbled over a 3 cm Az glauberite-xl floater for 1 euro, then 5 perfect double terminated Quarz-xls with organic inclusions for 1 euro, and so on... not to mention some Corocoro material... that material was just lying there in a box, screaming "people don't see me, please take me". Well... One should always help others, so I took the material home. Another advantage of collecting "floaters" is, that usually the material is small. So when you fly to a mineral fair with handluggage only. Those little xls fit in your pocket, or in a wooden sigar-box :-)

Cheers! Frank

[Jordi Fabre]

Here are the columns about single crystals published by John S. White on the magazine Rock & Minerals:

https://www.rocksandminerals.org/

Thanks to Marie Huizing for the permission to reproduce these columns!


Columns about single crystals published by John S. White
on the volume 81, November/December 2006
of the ROCKS & MINERALS magazine

[Joan R.]

Here are another columns about the -hedrals published by John S. White on the magazine Rocks & Minerals:

https://www.rocksandminerals.org/

Thanks to Marie Huizing for the permission to reproduce these columns!


Columns about the -hedrals published by John S. White
on the volume 77, September/October 2002
of the ROCKS & MINERALS magazine

[Joan R.]

Here is a guest editorial about single crystals published by John S. White on The Mineralogical Record:

https://www.minrec.org/

Thanks to Wendell E. Wilson for the permission to reproduce the editorial!


Guest editorial about single crystals published by John S. White
on the volume 25, No. 5, September-October 1994
of the magazine The Mineralogical Record.

[Mick Cooper]

It seems to me that the basic problem of the term “floater” is the dichotomy between how it’s used and what it implies. The latter is easy – the item was created in suspension in a fluid. However, it’s usually used to refer to a single crystal or group of crystals with no apparent point of attachment. I have two problems with this: (1) the word “apparent.” (2) how to describe a specimen comprising crystals on a piece of matrix that overall has no point of attachment?
Take no. 1 first: there might be – or possibly have been - a point of attachment that is no longer obvious. Perhaps it is too inconspicuous to see. Perhaps the crystal was once attached, broke off and the broken part was healed by further growth. Is this a “floater”? Sometimes the re-growth is obvious, sometimes I guess it may not be. I would count the famous Spanish pyrite cubes as unequivocal floaters since they must have grown in isolation unimpeded by the surrounding medium at the time of growth. Likewise certain feldspar crystals that must have formed in a melt.
But what of type 2? For example I have a very fine Dalnegorsk pyrrhotite crystal on a matrix of quartz crystals which is, as far as I can see (even under a microscope), complete all round. Similarly a piece of what I assume is vein breccia completely covered in vanadinite – there is likewise no apparent point of attachment on this either. I am certain neither formed while floating in the vein. So what do I call them to indicate their completeness? There is undoubtedly – to my mind - something special about such specimens, but calling them “floaters” implies a history that they palpably cannot possess.

[alfredo]

A true euhedral "floater", with no point of attachment can grow in various types of "fluid" environment, like the feldspar and augite phenocrysts in magma, already mentioned by previous posters, and the spanish pyrite crystals. In the latter case, I am assuming that the medium was a plastic carbonate-rich mud or clay rather than a true fluid, and the growing pyrites pushed the surrounding mud out of the way? (Has this been studied?) And the same would probably be true of other euhedral crystals that originally grew in clay - gypsum is a common example - that later hardened and became the matrix rock. Less commonly, the same can happen in the clay filling pegmatite pockets. I wouldn't call a spanish pyrite crystal a "floater" if it is still attached to its matrix. A euhedral crystal becomes a floater after it is detached from its matrix (otherwise it would be difficult to prove it was truly euhedral, except perhaps by x-ray!).

Other interesting ways some floaters grow: Small euhedral floaters can grow in the upward-flowing water of hydrothermal systems, which keeps the crystal in suspension until it eventually grows heavy enough to precipitate out. This must be the origin of floaters in ore veins. Another mechanism is crystals that grow in very fine-grained but highly porous host rocks. The crystal grows interstitially and does not push extraneous grains out of the way; it just incorporates them as it grows larger. This is common for crystals like boracite and danburite growing in the sugar-like anhydrite of saltdome caprocks. They are full of millions of tiny grains of their host rock, but I've never been able to understand how they manage to maintain a smooth surface as they grow - perhaps some surface tension effect pulls matrix grains away from the growing crystal surface?

I used to dream of having a good "floater" collection, but my good friend John White talks me out of the best ones, and all I get to keep are the crappy leftovers. Oh well, at least they went to an appreciative home ;((

Cheers,
Alfredo

[John S. White]

My good friend Alfredo wrote this: " otherwise it would be difficult to prove it was truly euhedral." I am not sure what he meant. A crystal is either euhedral or it is not, depending upon how one might limit one's defintion of euhedral. Take a look it at. Is it bounded on all sides by crystal faces? If so, it is euhedral. Where we run into difficulty is if one, like myself, prefers to limit euhedral to crystals that have grown in a semi-rigid or liquid medium, like a magma or a metamorphic environment experiencing high temperatures and/or pressures. Garnets in a schist are, to my way of thinking, euhedral. Floaters in a pegmatite are not. But, then, I am a purist and old-fashioned to boot. I like definitions to mean something.