[Yoritomo]

Hello!

     I'm completely new to the forum and my knowledge of Chemistry are very limited,so I decided to ask the experts(you).

     I have the following question:Does Silica Gel(colored with Cobaltoan Chloride) attack Calcium Carbonate (CaCO3),Copper Iron Sulfide(CuFeS2),Iron Persulfide(FeS2),Lead Sulfide(PdS) and/or Zinc Sulfide((Zn,Fe)S)?

     To describe better,I used a small bag(sealed) of semi permeable material which contained silica gel beads (colored with CoCl2 as an indicator) to protect mineral specimens of humidity.The minerals are the chemical compounds I listed above in solid crystalized form.The bag of Silica gel and the mineral crystals were not in direct contact.

      If my informaion is right,Silica gel is the porus form of Silica=Porus form of Silicon Dioxide(SiO2).This is the formula of the mineral Quartz,which doesn't attack the other minerals.But CoCl2 is a Lewis acid and I'm afraid it could have reacted with some of the minerals listed above.

       PLEASE!!!Could someone give me a scientific answer?Could this Silica Gel react with any of these chemical compouds EVEN IN MOLECULAR LEVEL?If it could,how long would it take to START the reaction in molecular level(I mean even not visible for me...)?


               Thank you all very much in advance and have a happy holiday!

                             -Kostas.

[Arkcon]

If they are not in contact, then they can't react.  They can be bought into contact, or if wet, enough will dissolve to start a reaction, but thats about it.  I assume the vapor pressure of these solids is low enough to prevent contact in the vapor phase.  The term "even in the molecular level" is, pretty much, meaningless in the sense you use it here, unless you care to define it.

Now, these pure crystals of yours, they may exist as hydrates.  If you were tyo use a more vigorous dessicant, like anhydrous CaCl2 (with or without the ppm CoCl2 indicator, ) you might damage the crystals.  Silica gel is probably gentle enough, but you should continually monitor your collection.

P.S. Are they quite large crystals?  And can you host pictures of them.  I used to enjoy trying to grow crystals as a kid.  Minimal success, however.

[Yoritomo]

Hello!

       hank you very much for the answer!

       Even in molecular level:I mean that the reaction has started,even if I cannot see it.Mineral specimens like Calcite(Calcium Carbonate) can be dissolved very easily in many acids.However,it should take more than half an hour to be able to see a difference on the specimen(crystal luster is gone,spots on the surface of the crystals etc.) if you try to dissolve it in non-concentrated citric acid,although the reaction has started ealrier in a molecular level(non-visible parts have started to react).

       The specimens are natural,not grown by me.Sorry,I cannot add photos(I have no camera)but I can direct you to a web page where you can see thousands of specimens.

        www.mindat.org (please delete this and excuse me if this is illegal and I shouldn't post it!If so,accept my apologizes).

        I am worried about the vapours of the compound!If molecules could "travel" 30 cm away they could reach the specimen and start a reaction.How long would it take for such a reaction to start?(approximatelly).

        Which of the minerals are in danger?Which is the aggressive compound,Silica or the Cobaltoan Dioxide?

         
        Is time and / or concentration factors of such a reaction?

       I have removed the bag of the specimens case.Does this eliminates the possibilities of future reaction?
Thanks a lot once again!
                   -Kostas.

[Mitch]

You sound overly worried about nothing, especially if they were stored in plastic away from direct contact.. The only way to really know, is to conduct an experiment. A better question is why are you so worried, what do you plan on using the minerals for?

[Yoritomo]

Hello again!

        Mitch,thank you for your reply!The plastic bag was the bag of the Silica gel.I got it from my new pair of shoes.This bag is semi-permeable,so water mollecules can pass through it.If the size of the CoCl2 molecules is bigger than water molecules,then yes,everything is safe.But if not,I worry that these molecules have attacked my specimens.

         Conducting an experiment with my poor knowledge on Chemistry and my poor equipment wouldn't help.But,please,suppose an experiment.

         The specimens form a collection.I do not use them for something.It's a common hobby,like collecting coins.The better you store some specimens the more you have them.There are minerals very fragile and sensitive to acids(like Gypsum-it dissolves even in distilled water!!!),while others cannot be dissolved even in very strong acids (like Beryl- Emerald is the green variety of Beryl).

          I want my specimens to be intact in any matter(even on molecular level-not only visually),and to achive that I have to control the conditions-humidity,acidity,light,temperature.

          An enviroment full of acid fumes can attack many of the different minerals.Humidity cause many of them to oxidate.Light causes in many cases loss of color(Amethyst loses color very easily because of sunlight).Low temperature makes some mineral crystals brake!You see,depending on the type of the specimen,one can be very fragile or less.

           Now,on the problem:so you think that vapours couldn't reach the specimen?

           Btw,to give you some info,Silica Gel beads have a blue center( a smaller sphere inside the Silica bead).This is the Cobalt Chloride coloration.The bead turns colorless and transparent when I add a drop of water.Then,when I heat it it turns blue again.

            Thank you VERY much!
                     -Kostas.

           

[Mitch]

In general, you only need to store materials as stringently as your experimental procedures can tell the difference. Since this is just hobby collecting, you are likely freaking out over nothing.

I've stored a huge variety of chemicals in the same dessicate material you've described above with no interfering chemical reactions occurring.

Although, this is a chemistry forum, this is really a more of a geology question and chemists wouldn't be the best people to ask.

[Yoritomo]

Hello!

      Mitch, Geochemistry is actually the field of Chemistry that specializes on minerals chemistry.However,silica gel is a product mostly known to chemists.That's why I added the chemical formulas of my minerals.The fact that these are natural crystals doesn't mean they are not chemical compounds and they do not behave like ones.

      The question may sound freaky,but it's important.This may be just a hobby,but these specimens are expensive and unique.For example,you may pay $4000 for a very special specimen of Galena(PdS) and see the luster gone in 3 years because of the humidity.The price goes at $40 or less.

      I'm very sorry if I occupied the forum with an irrelative question,I just felt I could find answer to a complicated question and I am so far very satisfied-quick and responsible answers!If I disturb you,please erase the topic and accept my apologizes.

      Thank you again for your help.Any more opinions or usefull info on the material?

      -Kostas

     

       

[Borek]

I'm very sorry if I occupied the forum with an irrelative question,I just felt I could find answer to a complicated question and I am so far very satisfied-quick and responsible answers!If I disturb you,please erase the topic and accept my apologizes.

Question fits forum profile OK, if Mitch asked for details that's most likely because people very often ask questions that are not addressing their problems. Clarification often helps to find out what they are really looking for.

I bet Arkcon is right - if the solids are not in contact and the humidity is low (should be in the presence of blue silica gel) you are on the safe side. If humidity can pose a problem, avoid semi-permeable foil.

[Yoritomo]

Borek,thank you for your reply!It's my fault actually.I should first ask about the gel and then ask about the reaction with the compounds.

     I'm not sure about the humidity.When I opened the bag the beads where colorless if I remember well.This means the humidity was high.

     I don't understand the answer.Are you mentioning the humidity as a dissolvent for the CoCl2(which as an acid could evaporate and its particles could react with the minerals) ,or as H2O particles that would attck the sulfides?

      Thank you very much!
               -Kostas.

[Borek]

I'm not sure about the humidity.When I opened the bag the beads where colorless if I remember well.This means the humidity was high.

If they are with CoCl₂ they are blue when dry and pink when wet. If they are colorless, thaey don't contain CoCl₂.

I don't understand the answer.Are you mentioning the humidity as a dissolvent for the CoCl2(which as an acid could evaporate and its particles could react with the minerals) ,or as H2O particles that would attck the sulfides?

Latter only.

[billnotgatez]

If it is OK with the originator we can move this to Citizen Chemist section.

[Yoritomo]

Hello!

       The beads are purplish blue when dry and turn transparent(colorless) when saturated with water.I have no idea if this is very very light pink,but I guess an indicator job is to be obviously colored,so they are probably not colored with CoCl2.If you have any idea which is the indicator,please describe it.


        No problem at all moving the topic,you know better where its place is!

        Thank you all so much for your answers!
                    -Kostas.
       

[billnotgatez]

I have had a little exposure to rock hounds. In most cases they just keep there finds in a cool dry location and not in contact with other items. Since none of what you have seems volatile I would assume they would not interact unless in direct contact.

You sound as if you are located in a lab where there are volatile acids.

[Yoritomo]

Hi there!

          Well the room where I keep the specimens is just a room of my house and several chemical compounds are here and there.Many specimens need chemical treatment to look better(they come out of mines full of mud and clay,so they have to be secondary prepared to be exposed in most cases).So I need to keep acids.


             I am located in Bulgaria and I collect Bulgarian minerals(having the chemical formulas I described).Unfortunatelly,these are some of the most sensitive species-sulfides and carbonates.

           Recently I have removed any chemical compound from the room and I keep the acids (HCl,HF,H2SO4) at the balcony.

           Rockhounds are different than other collectors-they tend to be more tolerant about the condition of their specimens.Most collectors search for pristine specimens only-not treated impropperly!

           A house is like a lab-bleach is very dangerous as many other chemicals usually used for cleaning.Acetic and Citric acid are also present.Museums usually have better facilities,providing optimal conditions for the specimens.Some very rich collectors can afford simillar facilities.

           Thank you very much!
                     -Kostas.
           

[billnotgatez]

what if you put your specimen in a sealed jar