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Techniques for CollectorsSolubility of minerals
21st Dec 2011 17:37 UTCReiner Mielke Expert
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
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
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
21st Dec 2011 23:33 UTCReiner Mielke Expert
That would be the scientific way of doing it but it would not be very practical.
22nd Dec 2011 13:17 UTCJohannes Swarts
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
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
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
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
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
if the formula/literature is a "secret of state", write me a private mail.
Greetings
Georg
28th Dec 2011 10:31 UTCAlfredo Petrov Manager
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
Is Ice soluble in water? Or does it just melt?
28th Dec 2011 12:39 UTCReiner Mielke Expert
28th Dec 2011 16:40 UTCSteve Hardinger 🌟 Expert
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
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
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
28th Dec 2011 17:59 UTCMichael Hatskel
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
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
28th Dec 2011 18:50 UTCAlfredo Petrov Manager
28th Dec 2011 19:52 UTCReiner Mielke Expert
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
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
28th Dec 2011 21:31 UTCAlbert Mura
28th Dec 2011 21:53 UTCAlfredo Petrov Manager
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
28th Dec 2011 22:02 UTCMichael Hatskel
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
29th Dec 2011 16:31 UTCDonald Peck
OOPS! I wrote this before reading page 2.
18th Jun 2012 18:56 UTCDavid Martz
18th Jun 2012 19:14 UTCAlfredo Petrov Manager
18th Jun 2012 20:12 UTCUwe Kolitsch Manager
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
18th Jun 2012 21:06 UTCReiner Mielke Expert
19th Jun 2012 00:31 UTCBart Cannon
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
19th Jun 2012 01:39 UTCDon Saathoff Expert
Don
19th Jun 2012 01:51 UTCTom Tucker
19th Jun 2012 02:28 UTCBart Cannon
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
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
19th Jun 2012 04:07 UTCHenry Barwood
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
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
19th Jun 2012 13:58 UTCBart Cannon
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
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
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
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
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
20th Jun 2012 16:22 UTCEmanuele Costa
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
12th Jul 2012 22:37 UTCŁukasz Kruszewski Expert
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
I have encountered similiar problems with other minerals.
13th Jul 2012 13:22 UTCOwen Lewis
-------------------------------------------------------
> 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
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
17th Apr 2013 03:00 UTCDoug Daniels
17th Apr 2013 16:17 UTCDonald Peck
18th Apr 2013 00:36 UTCRob Woodside 🌟 Manager
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
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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Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
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