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Techniques for CollectorsSolubility of minerals

21st Dec 2011 17:37 UTCReiner Mielke Expert

Before anyone gets on my case, I am well aware that there is a need to quantify what solubility means with respect to its use in identifying a mineral. I am also well aware that solubility in most cases cannot be used to positively identify a mineral, however for those of us who do not have the resources to resort to sophisticated and expensive methods, it can be a useful tool in narrowing down the possibilities. Trouble is that most of the data on the solubility is not quantified and if it is, not in a practical way. However I am hoping that some agreement can be reached on at least one term, insoluble.

Anyone have any ideas on what that term means in a practical sense. Say for example, how long a sample can be in a solution before it shows any changes in order to be called insoluble? Or? Someone must have some idea since that term is and has been so commonly used in mineralogy.

21st Dec 2011 20:16 UTCGeorg Graf

Hi Reiner,


do a mineral in a fluid, e. g. water: If a day later Your spezimen is still there and You can not see any damage/solution traces/etched away edges or something like that, it is "not soluble" in the test fluid. That´s my practical definition.


Greetings from Goslar


Georg

21st Dec 2011 20:22 UTCReiner Mielke Expert

Hello georg,


I would agree with that but what about 12 hrs later? When mineralogists do their solubility tests how long do they wait? Is there a standard period of time for that?

21st Dec 2011 23:11 UTCSteve Hardinger 🌟 Expert

I'm sure this won't help, but a chemist defines solubility in terms of amount of solute per volume of solvent, at a given temperature and pressure. We (the chemists) define solubility as an equilibrium phenomenon, and not a kinetic (i.e., rate at which it happens) phenomenon.

21st Dec 2011 23:33 UTCReiner Mielke Expert

Hello Steve,


That would be the scientific way of doing it but it would not be very practical.

22nd Dec 2011 13:17 UTCJohannes Swarts

Hello,


Interesting thread...


A question for the experts - how soluble is lanthanite-(La)? I have nice micro crystals of this mineral, and they often seem to have a dusting of clay on them. I'm tempted to soak & rinse them, but have read (somewhere) that this mineral is fairly soluble. I've already discovered that ultrasonic cleaning is NOT recommended - the crystals mysteriously disappeared, even after only a few seconds of treatment.


Any thoughts?


Thanks in advance,


Hans

22nd Dec 2011 15:10 UTCReiner Mielke Expert

Hello Johannes,


This summer I found what I think is Lanthanite-Ce with a high La content (EDS analyzed) and I washed it with water and did not observe any change. Dana says it is not soluble in water so I would say go ahead and wash it. However you may loose some of it if it is not well attached to the matrix, mine was well attached so there was no problem.

23rd Dec 2011 15:55 UTCGeorg Graf

Hi Reiner,


chemists, mineralogists and others define solubility as a quotient: max. mass of mineral soluted in 1 l fluid, mostly water.

They do not attend how long time is necessary to reach this max. value of soluted substance. They obtain this values mostly by the invers way: They mix a solution from which the "mineral" is precipitated; and analyze the fluid.


There are minerals not soluble in water, as Quarzt. - Easy solubable in water, as halite. After 1 day in water your spezimen is "disapeared" = soluted in water. Or at least You can see etched away edges e. c. t. - Minerals as Selenite, Anglesite e. c. t. are "a little bit" soluble in water. So far as I know, there is no standart procedure to test this. You can wash them in water without any damage. You can find them also in a climate with rain, as in the Harz Mountains. In good books for mineral collectors You find no list about solubility of minerals. But at some minerals, as Halite, a note: "soluble in water"; at some a note "soluble in acetic acid by generation of CO2-gas", as Calcite; at some "soluble in KOH-solution" as Anglesite.


My proposal: Test Your spezimen 24 h. But why not just 12 h; or 48 h: I can not tell You any reason. - A further possibility: Make a test with a surely analyzed mineral; and compare Your doubtly mineral by operating it in exactly the same way.


Hope this helps a little bit. Merry Chistmas and good luck in the new year! Greetings from Goslar


Georg

23rd Dec 2011 22:23 UTCReiner Mielke Expert

Hello Georg,


The reason I am asking is to try and make some sense out of the published information. If a paper says it is insoluble what does that mean? I would agree that if there is no change after 24 hours it is insoluble but does everyone do it that way? Maybe someone who has published such information can enlighten us. Unless one has a confirmed sample it is not possible to compare and I have very few confirmed samples. RUFF would be the perfect project to provide standardized practical solubility information.

28th Dec 2011 09:43 UTCGeorg Graf

Hi Reiner,


in the strictest sense "insoluble" means: 0,0000000000000 g are soluble in 1 l water. I think, diamond and graphite are in this sense "insoluble" in water. - Baryte, which is normaly called "insoluble" is a very little bit soluble in water. But normaly You can not realize that solubilty. -Maybe Your literature is not exact at that point. Is the author still alive? Ask him, what he wants to say. Maybe the author himself do not know, how inexact the term "insoluble" can be. Is/was he a chemist, or an amateur?


Or give me the chemical formula, and I tell You what I think about. Or can You post the literature You are thinking about?


Best wishes for the new year and greetings from Goslar


Georg

28th Dec 2011 10:30 UTCGeorg Graf

Hi Reiner,


if the formula/literature is a "secret of state", write me a private mail.


Greetings


Georg

28th Dec 2011 10:31 UTCAlfredo Petrov Manager

Actual measurements of solubility are usually done on finely powdered material, which will be much more noticeable than for an unpowdered chunk of a mineral specimen. A substance might be noticeably soluble in water (as a powder), and nevertheless a crystallized mineral specimen of it could easily be washed for a couple minutes without showing any visible alteration - Gypsum and fluorite, for example. Whether the mineral crystal has microscopic cracks or incipient cleavages that water could get into is also going to affect the outcome. And a "slightly" soluble mineral specimen that will easily survive a brief wash in cold water under the tap might not survive so well if using hot water, or using an ultrasonic bath.


Incidentally, I'm as frustrated as Reiner is by the lack of quantified information about solubility of minerals under different conditions. But I suppose in many cases this information will never be available unless serious amateurs undertake to do some experiments and publish the information. We can't expect professional mineralogists to do it - they're paid these days to describe and manipulate atomic structures, not publish information on cleaning, or kitchen identification techniques. The era of descriptive mineralogy is over. We serious amateurs can shed a tear for the bygone era, and then get off our arses and publish some of this 19th Century-style descriptive stuff ourselves.

28th Dec 2011 11:12 UTCJolyon Ralph Founder

This got me thinking.


Is Ice soluble in water? Or does it just melt?

28th Dec 2011 12:39 UTCReiner Mielke Expert

The problem for amateurs is access to confirmed samples. Most of what is available from dealers is not confirmed so even if you do the necessary solubility tests the question remains is this actually a sample of that mineral ( case in point, bobdownsite) If I had access to confirmed samples I would gladly establish a data base on solubility, it only takes a tiny speck the size of this "." under a microscope to determine solubility.

28th Dec 2011 16:40 UTCSteve Hardinger 🌟 Expert

Jolyon, the answer to your question is definitive.


A phase change is always required for solubility. A solid cannot exist as a solid in dissolved state. For example, NaCl (solid) becomes Na+ (aqueous) and Cl- (aqueous) when it dissolves. Ice also suffers a phase change (solid to liquid) before dissolving.


Any substance is miscible with itself (i.e., will always form a homogeneous solution in any ratio). When ice melts it (of course) becomes water, which is identical with its surrounds (i.e., more water). Therefore ice melts, then dissolves.

28th Dec 2011 16:43 UTCSteve Hardinger 🌟 Expert

Would quantifying mineral solubility be of much use to most people interested in minerals? I think not.


I don't think we need tables of data giving solubility in grams of mineral per liter of water at 25oC. Rather what would be useful is a more qualitative approach. For example: "When gypsum is placed in water at 25oC for one hour, we typically see..." or "when diamond is placed in water at 25oC for one hour we typically see..." ("...honey are you playing with my wedding ring again?")

28th Dec 2011 16:55 UTCDonald Peck

The solubility of chemical compounds is expressed as a solubility product. It is the equilibrium concentration of the compound in one liter aqueous solution at a specific temperature and pressure. It is a number. You can find more explanation than you probably want at http://en.wikipedia.org/wiki/Solubility_equilibrium and a table of values at http://www.ktf-split.hr/periodni/en/abc/kpt.html.


For barite, BaSO4, the Ksp = ++>4--> = 1.08 x 10-10 That is, the equillibrium molar concentration of barium multiplied by the molar concentration of sulfate in water is equal to 1.08 x 10-10 at 25oC and one atmosphere of pressure. If we are considering the equillibrium solubility of pure barite in pure distilled water, the molar concentration at 25oC and one atm of pressure will be the square root of the Ksp or about 1 x 10-5 moles per liter. That equates to 2.33 x 10-7 grams per liter.


The upshot is that we can express solubility in a number. And for simple molecular formulas we can find them in tables. However, I believe that for most minerals the values have not been determined and are not likely to be done. Solubility constants in acids can be calculated also, but are a bit more complex.

Foot note: my chemistry was long ago; so, Peter (or anyone) if I have made an error please correct me,

28th Dec 2011 17:03 UTCDonald Peck

I think Steve's suggestion makes some sense, as long as temperature and the fineness of powdering (screen mesh?) is stated. Both would have a significant effect on the result.

28th Dec 2011 17:59 UTCMichael Hatskel

I agree that the lack of info on such a basic mineral property as solubility in water is very frustrating. Alfredo is right: measuring solubility is not as sexy as determining/refining the crystal chemistry of a mineral. On the other hand, knowing the crystal chemistry shall provide clues to understanding the solubility (in terms of the crystal lattice strength), but certainly not a substitute for experimentally measured solubility data.


Reiner,

In absence of the solubility data for a particular mineral, our best guess is to access the solubility based on the mineral chemistry.

Bobdownsite may be considered a mixed Ca-Mg orthophosphate (PO4) - fluororthophosphate (PO3F).

From the chemical properties tables for the relevant chemical compounds, we can see that

(a) Ca-fluororthophosphate is slightly soluble in water at room temperature, more so than the Ca-orthophosphate (apatite); and

(b) Mg compounds tend to be more soluble than the corresponding Ca compounds, so the presence of Mg is likely to increase the solubility.

Therefore, it is reasonable to assume that bobdownsite shall be slightly soluble in water at room temperature (25C). I would expect it to be slightly/slowly "affected" by water. That is roughly the same category of solubility as gypsum.

In practical terms: one shall use as quick a wash as possible and water as cold as possible.


Steve,

IMHO, calling ice melting in water a dissolution is a biiiiiiiiiiiiiiiiiig stretch. Dissolution process shall involve a heterogeneous interaction, i.e. the solute and the solvent shall be different compounds. Melting is a physical process; dissolution is a chemical process, where the solute and the solvent interact chemically. An incorporation of the water from melting ice into the surrounding water is a simple mixing, not a dissolution.

BTW, if the resulting combined water is frozen again, you are not gonna call it a solid solution, aren't you? ;-)

28th Dec 2011 18:09 UTCMichael Hatskel

Don,

One comment to what you wrote:

The solubility product is used for insoluble or poorly soluble compounds. You were right to use BaSO4 as an example.

For the soluble compounds, the solubility is expressed in terms of the solubility limit = solute concentration in a concentrated solution at a given temperature, and could be expressed in different numbers/units (g/L, M, N, etc.).

28th Dec 2011 18:27 UTCSteve Hardinger 🌟 Expert

I didn't say that melting of ice is a dissolution phenomenon. I said that the water (produced by the melting ice) dissolves.

28th Dec 2011 18:50 UTCAlfredo Petrov Manager

I interpret Reiner's original question to relate to solubilities in various acids at different concentrations too, not just water, so... lots of measurements needed. A very time-consuming task if done with any significant number of species. And although the results might be occasionally of marginal usefulness in mineral identification, they could be very useful to people doing mineral cleaning and preparation.

28th Dec 2011 19:52 UTCReiner Mielke Expert

The solubility product is difficult to determine and not very practical. Like Alfredeo said I am also talking about solubility in the common acid and alkali solutions. I am thinking of a particular size of particle say 0.5mm and how long it takes to dissolve in a specific solution at say 20C. What puzzles me is why mineralogists even bother to provide such sloppy solubility data, if you are going to do it then do it right!

For example: Bobdownsite, it is reported by; Tait, K.T., Barkley, M.C., Thompson, R.M., Origlieri, M.J., Evans, S.H., Prewitt, C.T., Yang, H. (2011) Canadian Mineralogist, 49, 1065-1078. that "Bobdownsite is insoluble in water, acetone, or hydrochloric acid." Well I placed a 0.5mm piece of Bobdownsite ( unconfirmed) in concentrated HCl at 20C and it completely dissolved in 20 minutes! Now if someone with a confirmed piece could repeat my experiment and let us know the results that would be just wonderful ( or send me a piece and I will test it). If everyone would spend a little time doing this we could come up with a useful database of solubility in Mindat. However Mindat would have to make it easier to add such information to their database and it would have to be standardized.

28th Dec 2011 20:25 UTCMichael Hatskel

Alfredo,

If we bring in the solubility in acids/alkalies, there is even more uncertainty about the term "solubility", because in many cases it actually means "decomposition" rather than "dissolution".

It is my understanding that when the literature simply says "soluble/insoluble in acids" or "in strong acids", it means just the acidic action, e.g. calcite in HCl. But does every reader know that it should not be extended to ANY acid, e.g. does not include HF (for silicates), HNO3 (for sulfides/sulfosalts), etc.?


That's why the all-inclusive term "affected/affected to a limited extent/not affected" may seem to be less accurate but also less confusing to describe applicable cleaning methods.


The nature of the effect needs to be known, of course: dissolution, chemical corrosion, unwanted coating formation, etc.

Simplified example: Halite NaCl is not considered acid-soluble but will dissolve in the water content of a dilute HCl acid. Therefore, halite is affected by dilute acids, so using them to clean halite is not recommended.


There are tons of valuable practical info in the Mindat forum threads on specimen cleaning and identification. I hope that there is a standard procedure in place for transferring that info to the mineral species pages or at least putting a link there.

Maybe in addition to referencing the threads on the species pages, all that info could be summarized in some sort of lists (tables), at least at a qualitative level, somewhat as an update to what Sinkankas did in his book?


For example, it might be helpful to have a Mindat list of minerals whose solubility in water is decreasing with temperature. Shouldn't be too many mineral species, but may be a good start.

28th Dec 2011 20:42 UTCReiner Mielke Expert

My understanding of solubility as used by mineralogists is any change in the original mineral or the solution it is in is an indication of dissolution, as such, one should note what the changes are. For example, a change in the color of the mineral, which would be extremely important for deciding how to clean a mineral.

28th Dec 2011 21:31 UTCAlbert Mura

Reiner, I'm not sure where that idea came from "solubility as used by mineralogists is any change in the original mineral or the solution it is in is an indication of dissolution", however, that is not the meaning of solubility. Solubility is measured, as other have said above. mass of a solute dissolved in a certain vol. of solvent or in certain cases a solubility product. In any case, a lot of pure chemicals (some of which are minerals) have their solubilities reported in the chemistry literature. As to water solubility I think you would find that most minerals, even as a powder, would not be very soluble and therefore not easily measured. Acids and bases are a different matter. An important issue in solubility are the conditions under which the rest is run (temp. etc.) and if they are not kept constant from one person to the next, you have a bunch of useless data that you can not be compare.

28th Dec 2011 21:53 UTCAlfredo Petrov Manager

"An important issue in solubility are the conditions under which the rest is run (temp. etc.) and if they are not kept constant from one person to the next, you have a bunch of useless data that you can not be compare." ...exactly, Albert. This is why solubility as currently reported in mineralogical literature by mineralogists is useless.


And of course, Michael, partial solution, decomposition, gelification, etc, will require additional description and explanation. And for purposes of ID, decomposition can provide more useful information than simple complete dissolution, especially if a coloured precipitate is left behind.

28th Dec 2011 21:56 UTCAlbert Mura

Adding to the confusion is the fact that most minerals are not pure substances and therefore one sample will not necessarily have the same solubility as another. I think that the difficulties in measuring solubilities of minerals speaks more to the lack of data in that field than other less scientific reasons.

28th Dec 2011 22:02 UTCMichael Hatskel

Reiner,

Change in color is not necessarily caused by dissolution.

Leaching of a color-causing component from the specimen surface may qualify as a partial dissolution.

An opposite example: when IronOut solution is too concentrated and hot, the iron stain coating may change its color from yellow to green because the ferric ions (Fe3+) get reduced to ferrous ions (Fe2+) while remaining in place as opposed to getting dissolved into the IronOut solution. Same color change to green may happen to the Fe-bearing silicates in the specimen. Here you have it: color change caused by a chemical redox reaction, not dissolution.

As I suggested before -- affected, not soluble.

28th Dec 2011 23:44 UTCReiner Mielke Expert

Where I get my notions on solubility is from Dana's textbook of Mineralogy. In the section on solubility there is reference to changes in the solution. "partial solution is often shown by the color given to the liquid etc. ". This could only come about if something is removed from the mineral by dissolution. I cannot find any requirement in any mineralogy book that restricts the meaning of solubility to complete dissolution. Besides such a narrow definition would not be very useful. I suppose for what I have in mind a be better described would be the behavior of a mineral in a solution. This would provide far more useful information than strictly solubility.

29th Dec 2011 16:31 UTCDonald Peck

Michael, I agree. I don't think there is a problem with the readily soluble minerals. I think (but am not sure) that Reiner is more concerned about the solubility of the slowly soluble or slightly soluble minerals. Thanks for the comment.


OOPS! I wrote this before reading page 2.

18th Jun 2012 18:56 UTCDavid Martz

Being from the western U.S. the subject of solubility is rather significant to me for a couple of reasons. Most importantly, if you consider mineral identification to include keys from the environment in which a specimen was found, solubility is sometimes critical. Turquoise is a good example where the worldwide distribution reflects dry climates, due to its solubility and the way water is involved in its formation. Hint: Don't look for it in a jungle, and if you find something resembling turquoise in a wet climate, focus on other blue copper minerals first, in particular the less soluble ones. Second, in terms of pseudomorphs. Near the surface, less soluble minerals replace more soluble minerals as a rule, and this is occasionally an important clue when trying to determine why a mineral has taken a crystal form it is not supposed to exhibit. It is also useful for rejecting certain replacements, and therefore mineral possibilities. I have seen a few pseudomorphs described where the replacement was not feasible, hence the original mineral was not what the collector thought. Finally, solubility is vital in the ordering of some minerals in a deposit. All that being said, the laboratory use of solubility for identification has limits, but also unexplored potential. As an example, if you had tiny crystals of something you thought was a carbonate, you could dissolve equal amounts of it it water and in carbonated water. If it is a carbonate, it should dissolve slowly or not at all in the carbonated water. Similar tests could be done using saturated epsom salt water (for sulfates), but some standard runs with known minerals would be needed for comparisons.

18th Jun 2012 19:14 UTCAlfredo Petrov Manager

David, I fear that solubility is a much more complex topic than that... Turquoise, for example: The 2 best specimens I have are from Virginia, which is horribly humid in summer, and Belgium, where it rains every day, so one cannot say that this is just a dry climate mineral. And the most common carbonate, calcite, will dissolve much better in carbonated water than in pure water.

18th Jun 2012 20:12 UTCUwe Kolitsch Manager

"The 2 best specimens I have are from Virginia, which is horribly humid in summer, and Belgium, where it rains every day, so one cannot say that this is just a dry climate mineral."


The climate may have been completely different while the mineral has formed (hundreds, thousands, millions of years ago).

18th Jun 2012 20:29 UTCAlfredo Petrov Manager

Indeed, Uwe, that's right, but it doesn't dissolve away and disappear when wet now, so not identifiable by solubility, which is apparently what David would like to use as a classification tool. Gypsum would perhaps be a better example of a slightly soluble mineral that forms equally well in dry and wet climates. (The first gypsum crystals I ever found, as a kid, were in a clay pit in England.)

18th Jun 2012 21:06 UTCReiner Mielke Expert

From the perspective of a mineral, climate is irrelevant, it is the conditions of the fluid that the mineral is in contact with that is important. Clay has a very low permeability and therefore allows little movement of fluids, this preserves the gypsum crystals regardless of the climate. Gypsum that grows in a salt flat is in water saturated with gypsum so in fact they are wet even though it may be a dry climate. Climate is only important in that it may facilitate the right conditions for fluids from which the minerals can form, however these same conditions can occur in different climates.

19th Jun 2012 00:31 UTCBart Cannon

I would love to know how to dissolve barite.


In forty years of fussing, I've never even been able to even frost a crystal face with anything.


I have some silvers enclosed in white barite.


Bart

19th Jun 2012 01:03 UTCAlfredo Petrov Manager

Try molten sodium carbonate. I don't think it will hurt the silver, but I'm not sure about that. :-)

19th Jun 2012 01:39 UTCDon Saathoff Expert

Bart, be careful though......Sodium Carbonate melts at ~851C and silver at ~961C.......if you have a muffle furnace in which you can control the temp you should be OK.


Don

19th Jun 2012 01:51 UTCTom Tucker

Bart, so much for dissolving barite, oops, baryte - how do we move enough solute saturated with barium and sulphate through something as impervious as the Pierre shale and its equivalents to precipitate those magnificent crystals at Elk Creek, and elsewhere?

19th Jun 2012 02:28 UTCBart Cannon

Tom,


That is a good point. Barite crystals are everywhere, but quartz crystals are even more common.


One could place either in a glass of water and neither would dissolve in a 100 million years.


Hydrothermal conditions can do wonders for mineral precipitation.


But what about Norman, Oklahoma and its barite roses ?


I think those things are still forming in soil.


Bart

19th Jun 2012 02:46 UTCHenry Barwood

Sorry to jump into this topic, but many of the barite, celestite, etc. minerals that are shale or nodule hosted form from expelled solutions as the shale consolidates. The same is true of lime muds. These have nothing to do with weathering at all.


For years I had people claim that the Virginia turquoise crystals were forming rapidly on the dumps. I searched for years for anyone who could provide me with an example of the oft cited "turquoise crystals growing in a root" and drew a blank. It has been a long time since I calculated a solubility constant, but most minerals are a lot more complex than just "water soluble".

19th Jun 2012 03:55 UTCTom Tucker

Yes Bumpi, but even the water displaced during sediment consolidation can't account for precipitating all that barite (baryte) can it ? I don't have my Handbook of Chemistry handy, but I think it'll take a bunch of water to precipitate even a single little barite crystal. Are complex ions involved ?

19th Jun 2012 04:07 UTCHenry Barwood

Hi Tom,


There is a lot of water in mud. As it is compressed, not only the water, but cations and anions that were absorbed on the clays, are expelled. If there are pathways present, the fluids migrate into new areas. If they reach a point where the eH and/or pH changes, minerals will precipitate. Imagine the water contained in a 20 foot thick layer of mud that compresses to a foot thick layer of shale and you will have some idea of the scale of this process. Remember that things like barite are not moving as Barium Sulfate, but as soluble Barium complexes and Sulfate anions. When they reach a favoralbe site, you get barite.


Deeper burial introduces heat and additiional release of ions. The hydrothermal (or very low-grade metamorphic zone) is one of our most important ore-formers.

19th Jun 2012 06:30 UTCBart Cannon

Haven't we all wondered how long it takes a crystal to grow in the natural environments ?


Other than evaporate minerals, as far I know. NOBODY knows !


Famed Arizona mineral dealer Dick Jones knew exactly how long it took a bloedite crystal to reach a saleable size in one of his hatchery holes out in the Salton Sea, I think it was. He would dig a pit and return to collect his progeny when they reached maturity..


I am probably wrong about both the dealer's name and his hatchery's name.


Bart

19th Jun 2012 09:05 UTCRock Currier Expert

The locality for the Blödite is Soda Lake, Carrizo Plain, San Luis Obispo Co., California, USA. I went collecting with Dick Jones and Gary Novak there for Blödite and nether of them said anything about hatchery holes. Most of the ones we found were less than two inches in size. We each came away with several hundred crystals for our effort. The really big ones were found by Art Eadie, a petroleum geologist who collected rare species and lived in Taft, California, a stones throw from the locality. He even had a claim on parts of the lake. He went to hi maker without telling anyone about where and how he found the giant Blödite crystals on the lake.

19th Jun 2012 13:58 UTCBart Cannon

Rock,


I sure wish I had hung onto one of Art Eadie's business cards though I certainly could not have shown it to my mother.


I forgot about the Dick Jones / Gary Novack connection. Many curious stories there including puzzling smoky quartz..


Maybe at a later date, but I'm pretty sure that there was some kind of hole digging going on and harvesting from them.


I can only barely remember what Dick Jones looked like so maybe I'm remembering something else.


I think he used to hire a plane to follow his competitors into their locations, or maybe it was the other way around.


Bart

19th Jun 2012 16:50 UTCReiner Mielke Expert

Hello Bart,


Assuming your sample of barite and silver has enough silver in it to stay in one piece, you should be able to remove the barite by heating and quenching the sample in cold water, barite will crumble silver will not.

19th Jun 2012 21:24 UTCBart Cannon

Reiner,


Thanks !


Heating and quenching was my method of first choice. It was standard procedure for removing basalt from Keeweenaw coppers.


It didn't work on the silver and barite. Maybe I should get the specimens hotter.


Bart

20th Jun 2012 00:52 UTCJeff Weissman Expert

Bart


When removing catalyst washcoat from honeycomb monoliths, we first dip in liquid nitrogen, followed by heating in a flame. Takes a few cycles, but eventually the washcoat flakes off - you may want to get your barite much colder and see if that works for you.

20th Jun 2012 04:29 UTCBart Cannon

Jeff,


It just so happens that I filled my LN2 dewar today. Of course I use it for my EDS system, but people show up to have their warts removed. A very notable Mindater has done so, but demanded a triple treatment. It worked out.


Maybe I'll dip a silver/barite in.


My dewar weighs 51 pounds when full and it strains me to get it into my car.


There was a 120 pound kid waiting to have his dewar filled. It weighs 100 pounds when full, yet he hefted into his Volvo without difficulty.


His name is Daniel Troberg of Robison Engineering. He uses LN2 to cool down computer processors to put them into overdrive without burning out the microscopic transistors. He told me he holds second place on Earth for processor speed. He is about 23 but already bored with his career.


I think I'll hire him to re-design my TV processor scanning system in my electron microprobe.


Bart

20th Jun 2012 10:20 UTCRock Currier Expert

I think somewhere I have one of Art's business cards.If and when I find it Ill save it for you. I don't think they collected Blödite more than once of twice because like the thenardite, there was little market for the stuff and it was a lot of work for the little return you could get out of the stuff. I had a 4 inch flat pilled full of Blödite crystals for years and was not able to sell them. I don't know what happened to them May have sold them to the mineral of the month club or something. Sam Nasser of Arizona told of visiting Dick Jones at his home in Casa Grande one time and finding him in his garage with an old dental x-ray unit irradiating Japan law twins from New Mexico to turn them smoky. I don't know if that story was true or not. I'm not convinced that a dental x-ray unit would turn quartz smoky.

20th Jun 2012 16:22 UTCEmanuele Costa

Hi to All,


after reading the very interesting post I would like to return to the original question of Reiner and submit my very poor experience.... There are no practical and easy way to determine the real solubility of a mineral, except for that ones that are READILY and VERY soluble like halite.


I normally work with poor-soluble minerals, like calcite and gypsum, (but they are not insoluble! calcite dissolve in destilled water for about 0.02 g/l, and gypsum about 2 g/l depending on temperature and other various factors) studying the precipitations of these substances, changing the environmental conditions. If one want to really knows if a small amount of a mineral dissolve in water, this one should use analitical techniques like atomic absorption flame fotometry or titration or even more complicated ones. No way to determine, in a small fragment of a mineral, in few hours, if something can dissolve. Surely something dissolve, but if you dont see strong variations on the surface of the crystals, like specular surface becomed hazy or etch pits or rounding of the edges, you cannot state that the minetral is really insoluble.


So, for a poor rockhound with a poor homemade laboratory is difficult to affirm that the substance he found is really insoluble. One of the simplest thing I can imagine (but you need at least 0.1 g of mineral or so) is to crush the mineral in fine powder - some like sugar - put it in a little glass vial with 10 cc of destilled water, leave it - better under agitation - for some 24/48 hour AVOIDING CONTACT WITH AIR (rubber stop), leave it standing calm and quiet until the liquid portion on top is very clear (not cloudy, no suspended material) and collect that clear portion with a glass pipette (some 1 ml).


You will after put this 1ml test drop on a very clean glass surface, and evaporate it gently avoiding contact with dust. If the drop leave evaporating a halo of solid material , this could be a suggestion that some of your mineral was dissolved. MAKE ALWAYS A REFERENCE TEST (NO MINERAL) with your destilled water: some of these are only deionized, and may be they have inside a lot of silica (sio2 in colloidal form).


BUT:


If you do this with some minerals, you could have a reaction with water and air oxygen - I.E. pyrite react a little with oxygen, and could form a little of iron sulphate, and this is very soluble - this is the reason why one should use rubber stop.


and if you have the formation of some colloidal suspension, you have material in water but this is not a real solution.


and you have to be sure that the sample you used for the test is very pure,


So the question is not so simply.




I tried to do my best with english, but please be indulgent with an Italian rockhound.


Best Regards to All


Emanuele Costa

Torino (Italy)

20th Jun 2012 18:28 UTCJeff Weissman Expert

Bart, I can sympathize with your hauling of LN2 dewars - I can remember "riding" them down the sloping hallways of Carnegie Mellon, in Pittsburgh, hoping not to crash into the wall at the end of the corridor - once they get going, even on a moderate slope, hard to stop all of that momentum, but I was much younger and less careful back then, and needed the occasional cheap thrill. But we are getting off topic.

12th Jul 2012 22:37 UTCŁukasz Kruszewski Expert

Hi!


In general, there is not such thing as INSOLUBLE material. The time when it passes into solution in form of ions depends on its chemistry. HgS and PdS are, e.g., two such cases, when the substance needs a PLENTY of time to pass into solution. But, believe me, it will pass. A man in our Institute did a research: he put cinnabar into pure water and analyzed the water for Hg after few years. The result was positive.


Regards!


Luke K.

13th Jul 2012 01:47 UTCReiner Mielke Expert

Thank you for your comments on solubility. I was not concerned with the actual solubility but relative solubility, that is any solubility that can be observed in a relatively short time ( < 24hrs). The reason for this is that such information can be very useful in helping identify minerals cheaply and quickly but this requires a database that is practical and accurate which we currently do not have. The main problem is that confirmed samples need to be used to establish such a database and those can be difficult to come by. For example, the published literature on Bobdownsite says that it is insoluble in acid. I asked the authors of the paper about this a year ago and got no response. Also no one seems to have a confirmed sample, although many dealers say they have Bobdownsite for sale (which would have been called Whitlockite a few years ago) but none of it is confirmed. I have such a "Bobdownsite" sample in my possession and when I tested it, it was readily soluble in HCl.

I have encountered similiar problems with other minerals.

13th Jul 2012 13:22 UTCOwen Lewis

Jolyon Ralph Wrote:

-------------------------------------------------------

> This got me thinking.

>

> Is Ice soluble in water? Or does it just melt?


It melts. The presence or absence of extraneous liquid H2O neither helps nor hinders the phase change. The necessary additive to effect the phase change is energy (applied at atmospheric pressure usually in the form of heat). The quantity of energy required to cause the phase change of a quantity of a pure solid material to its liquid state without any rise in temperature is a property of each material and is known as the latent heat of fusion. In the case of pure H2O at atmospheric pressure, the energy required to change one kilogram of ice to water with no rise in temperature is 334 kiloJoules.


The solid/liquid phase change is bi-directional. I.e. it takes the removal of 334kJ from 1kg of water to change it to ice. Energy transfer also governs transition between the liquid and gaseous state but for the same material the latent heats of fusion and vaporisation are different. In the case of H2O, the latent heat of vaporisation is 2260 kJ/kg.

16th Apr 2013 22:37 UTCElshami T

There is no such thing as the solubility of minerals in water. The great lord Kelvin himselt made the same mistake shortly before his death

when he tried to calcaulate the age of our earth using the amount of dissolved matter in sea water and the rate of solubility The result was about

20 000 years compared to about 4.5 billion years . Mineral forming elements do not go into solution in the the same proportion in which

they occur in the solid mineral. Thus, minerals decompose in water rather than dissolve in it.

17th Apr 2013 00:10 UTCRock Currier Expert

I never thought of it that way, but of course he is correct. I feel however that this argument will not change the wording that people use from Soluability to anything else.

17th Apr 2013 03:00 UTCDoug Daniels

It wasn't Lord Kelvin that did this calculation- he used heat flow and cooling of a molten Earth. I think Joly did the salt-into-the-ocean calculation, but didn't take into account the fact that dissolved minerals (yes-dissolved) can also precipitate back out of solution. The cycle can repeat many times, messing up your calculation.

17th Apr 2013 16:17 UTCDonald Peck

Minerals, like any substance, dissolve. Some completely and some hardly at all . . . but they do dissolve. They are chemical substances, albeit often quite complex, and obey the laws of chemistry.

18th Apr 2013 00:36 UTCRob Woodside 🌟 Manager

Doug is right. Kelvin looked at Laplace's nebular hypothesis and assuming a uniform mass distribution, calculated the energy released when it all collapsed from out to Neptune's orbit down into the sun. He assumed some probably reasonable heat capacity and got an initial high temperature. Then using the newly discovered law that energy radiated by the fourth power of the temperature and knowing the current energy flux from the sun, he found the Earth to be 40 million years old.


This was in line with Helmholtz' calculation a generation earlier. By that time the outflow rate of the major rivers as well as their solute load was known. From this data Helmholtz calculated the rate of addition of salt to the oceans and with today's concentration found that 40 million years of accumulation would turn fresh water into sea water.


Of course Kelvin knew nothing of thermonuclear reactions. He started his calculations by assuming that the sun was entirely made of coal and with the current energy output would only last 100 years, so he suggested gravitational energy as the source of the sun's energy. Similarly people were still arguing about the flood when Helmholtz worked and as Doug pointed out, the creation of dead seas and their final salt beds vitiates Helmholtz' idea.


What is a little troubling to me is that I tend not to believe any major result unless two groups have independently verified it. So at the end of the nineteenth century I would have criticised the geologists for suggesting that the Earth might be older than 40 million years.

22nd Apr 2013 13:50 UTCcascaillou

Here's some online ressource for solubility data:


http://www.mindat.org/article.php/553/Solubility+Data+on+646+Common+and+Not+So+Common+Minerals


There's also a french book which features solubility data for hundreds of minerals:


La grande encyclopédie des minéraux (editors: Grund)


When I test for solubility, I just remove a tiny grain (1mm is enough) of the mineral and let it sit at room temperature for 24H in hydrochloric acid.

If it remained unaffected, I might then place the grain inside a pyrex test tube, add a bit of hydrochloric acid, and boil it for a few minutes (when doing so, always slightly inclinate the tube so to orientate the tube mouth in a safe direction in case of projections. Wear safety goggles).

If these two tests didn't affect the grain, you might rince the grain with water and then repeat the 24h room temperature test using other acids (sulfuric or nitric), but I usually don't bother to.


I use acids from the hardware shop, without diluting these (as they are already diluted enough). Also, better stay away from hydrofluoric acid.
 
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