How many minerals have colorful salts?

[Kurious12]

Anyone have a clue as to how many minerals have colorful salts? The only one that I can find is iridium and if I google colorful salts, all I get is photos or articles about salt that has been dyed different colors. 

[exchemist]

18 minutes ago, Kurious12 said:

Anyone have a clue as to how many minerals have colorful salts? The only one that I can find is iridium and if I google colorful salts, all I get is photos or articles about salt that has been dyed different colors. 

Your question, as posed, does not make a lot of sense. Salts are just ionic compounds resulting from the reaction of an acid with a base. As most minerals are not acids or  bases as such, they can't really be said to have salts.  

Most coloured salts are compounds of transition metals. This, as I recall, is due to the presence of partly occupied d-orbitals, whose energy levels tend to be split, by the ions surrounding the meal atom in many of their compounds, in such a way that transitions between the levels involve energy in the visible region of the spectrum.

Well-known examples of coloured salts would include CuSO4 (blue in hydrated form, white in anhydrous form), CoCL2 (blue in anhydrous form, pink hydrated, FeCL2 (pale green) and so on. 

But maybe you are trying to get at something else?

 

[studiot]

1 hour ago, Kurious12 said:

Anyone have a clue as to how many minerals have colorful salts? The only one that I can find is iridium and if I google colorful salts, all I get is photos or articles about salt that has been dyed different colors. 

This is posted in Earth Science, where there are many disparate definitions of 'mineral'.

https://www.uky.edu/KGS/rocksmineral/minerals_definition.pdf

A sub class of these definitions, which I assume you are referring to concern chemical compounds of definite proportions and sometimes crystalline definite structures which form the ingredients that make up the rocks, such as olivines, quartz, feldspars.

Minerals can be pure metal (eg native copper) , metal or non metal compounds such as oxides (eg hematite), silicates (eg garnet) , carbonates (eg calcite), sulphides etc etc.

Of these, some can truly be called salts and some of these are indeed coloured, for instance

Azurite  - copper crbonate is 'azure blue.

Chromite - the iron salt of chromic acid is black

Wulfenite - the molybdate salt of lead is yellow/orange/brown

Most coloured minerals are not salts though and many arise from replacement metal atoms in a silicate matix.
Silica (silicon dioxide) is itslef colourless but impurities create many coloured varieties wg rose quartz.

 

[Kurious12]

Thanks guys, this helps a lot. I was just trying to find something that might help to explain the colorful salts of iridium.

[exchemist]

1 hour ago, Kurious12 said:

Thanks guys, this helps a lot. I was just trying to find something that might help to explain the colorful salts of iridium.

Are they especially colourful? I think Ir compounds are mostly oxidation state +3 or +4 and quite a few of them are black or dark brown. But frankly Ir is not an element I know much about. Which salts do you have in mind? 

[Kurious12]

On 5/29/2022 at 2:17 PM, exchemist said:

Are they especially colourful? I think Ir compounds are mostly oxidation state +3 or +4 and quite a few of them are black or dark brown. But frankly Ir is not an element I know much about. Which salts do you have in mind

I was trying to make sense of what I was seeing in the photos below, I kept seeing these colors in several of the closeup photos that were taken of crystals. No one could say for sure what was causing this, a high level of iridium was detected in this stone so I was told maybe what I was seeing was being caused by the colorful salts of the iridium in the stone. I can't find anything on colorful salts of iridium, the best info I've come across about colorful salts in minerals is what I've been given on here, so thanks.

[exchemist]

4 hours ago, Kurious12 said:

I was trying to make sense of what I was seeing in the photos below, I kept seeing these colors in several of the closeup photos that were taken of crystals. No one could say for sure what was causing this, a high level of iridium was detected in this stone so I was told maybe what I was seeing was being caused by the colorful salts of the iridium in the stone. I can't find anything on colorful salts of iridium, the best info I've come across about colorful salts in minerals is what I've been given on here, so thanks.

These look like high magnification pictures of the same pyrite specimens you showed us earlier. The iridescent colours look to me as if they could be due to interference fringes, caused by diffraction arising from surface irregularities. You might be able to test this by seeing if the colours change as you move the source of illumination, so that the angle of incidence of the the light changes. 

Edited May 31, 2022 by exchemist

[studiot]

48 minutes ago, exchemist said:

These look like high magnification pictures of the same pyrite specimens you showed us earlier. The iridescent colours look to me as if they could be due to interference fringes, caused by diffraction arising from surface irregularities. You might be able to test this by seeing if the colours change as you move the source of illumination, so that the angle of incidence of the the light changes. 

+1

[John Cuthber]

I think there's some misunderstanding(s) here.

Irises (both the flower and the coloured bit of the eye); iridium and  iridescence all get their names from ίριδα the Greek for rainbow.

Iridium was named after the fact that many of its compounds are strongly coloured. Chromium was similarly named (from χρώμα)

But iridescent minerals do not typically contain much iridium (and nor do irises).

Iridium is rather rarer than gold.

 

[Area54]

3 minutes ago, John Cuthber said:

Iridium is rather rarer than gold.

 

Indeed. The unusually high concentrations of iridium, well above normal levels, at the Cretaceous -Paleogene boundary led to the identification of the Chicxulub impact that caused the extinction of most of the Earth's species, including the non-avian dinosaurs. If iridium were common we might still be puzzling over all that.

[sethoflagos]

On 5/31/2022 at 6:11 AM, Kurious12 said:

I was trying to make sense of what I was seeing in the photos below, I kept seeing these colors in several of the closeup photos that were taken of crystals. No one could say for sure what was causing this, a high level of iridium was detected in this stone so I was told maybe what I was seeing was being caused by the colorful salts of the iridium in the stone. I can't find anything on colorful salts of iridium, the best info I've come across about colorful salts in minerals is what I've been given on here, so thanks.

 

 

Pyrite is unstable in air, and frequently accumulates a tarnish of goethite - a hydrated Fe III oxide. Goethite is quite well known (in the jewellery trade and elsewhere) for the iridescence that can develop in the right conditions. 

Edited June 1, 2022 by sethoflagos

[exchemist]

1 hour ago, sethoflagos said:

Pyrite is unstable in air, and frequently accumulates a tarnish of goethite - a hydrated Fe III oxide. Goethite is quite well known (in the jewellery trade and elsewhere) for the iridescence that can develop in the right conditions. 

Bingo! Well done.

Prompted by your response to look up goethite, I found this: https://www.rockngem.com/iridescence-understanding-the-rainbow-in-the-mineral-world/ , which also explains the iridescence is indeed due to interference from microscopic surface irregularities.

So now it seems we have a fairly complete explanation. 

[sethoflagos]

4 hours ago, exchemist said:

Prompted by your response to look up goethite, I found this: https://www.rockngem.com/iridescence-understanding-the-rainbow-in-the-mineral-world/ , which also explains the iridescence is indeed due to interference from microscopic surface irregularities.

Interesting article! It's easier to see the common threads when a good mix of examples are explained in a single source.  

[Kurious12]

On 5/31/2022 at 2:38 AM, exchemist said:

These look like high magnification pictures of the same pyrite specimens you showed us earlier

Yes, this is all about the same pyrite specimen. I had taken several close-up photos under different lighting and would keep seeing lots of different colors. A few years back someone had me contact a Geochemist that has collected and studied pyrite from all over the world, he was a bit stunned by a lot of what I showed him, said that he had never seen anything like this pyrite. There were several metallic elements detected in this pyrite, I was told it could be anyone of them causing the colors, because iridium was detected at such a high level and known for its colorful compounds, I was told that I should start my research with iridium and work out from there. People kept recommending electronic scans but every scan I had done created more questions than answers. The last photo below is an actual xrf analysis that was done on this pyrite, everyone said that this could not be correct, so they calibrated the instrument and still got pretty much the same results. Thanks for all of the good articles, I've learned a great deal on here.

[exchemist]

3 hours ago, Kurious12 said:

Yes, this is all about the same pyrite specimen. I had taken several close-up photos under different lighting and would keep seeing lots of different colors. A few years back someone had me contact a Geochemist that has collected and studied pyrite from all over the world, he was a bit stunned by a lot of what I showed him, said that he had never seen anything like this pyrite. There were several metallic elements detected in this pyrite, I was told it could be anyone of them causing the colors, because iridium was detected at such a high level and known for its colorful compounds, I was told that I should start my research with iridium and work out from there. People kept recommending electronic scans but every scan I had done created more questions than answers. The last photo below is an actual xrf analysis that was done on this pyrite, everyone said that this could not be correct, so they calibrated the instrument and still got pretty much the same results. Thanks for all of the good articles, I've learned a great deal on here.

Suggest you try the test I recommended, by changing the angle of illumination and watching what happens to the colours as you do so. Rotating the specimen slowly may do the trick. If the colours are due to diffraction, as both @sethoflagos and I are proposing, you should see them changing. 

I think it unlikely that Iridium is responsible. The colours after which it was named were not those of minerals, but colours of the halides in various oxidation states when the element was dissolved in "marine acid" (HCl). The explanation of oxidation of the surface to goethite seems far more likely. 

[sethoflagos]

On 6/2/2022 at 9:57 AM, exchemist said:

I think it unlikely that Iridium is responsible. ... The explanation of oxidation of the surface to goethite seems far more likely. 

Important to point out that this does not exclude there being a significant iridium content in the sample. Merely that the iridescent surface coating has other causes.

Much of the world's accessible iridium reserves are in sulphide minerals, including pyrite, associated with some very particular geological structures. But in the absence of any information from the OP as to exactly where the sample came from or what other minerals and rock types it was associated with, the anomalous x-ray fluorescence data will probably remain just that. We have nothing else to go on. 

[Kurious12]

On 6/2/2022 at 1:57 AM, exchemist said:

Suggest you try the test I recommended, by changing the angle of illumination and watching what happens to the colours as you do so

Most of the specimen are too small to hold and rotate but what I have done is to take a bright light and moved it around to see what happens, the colors don't change, they just go from bright to dim, like in the last two photos below. I have from time to time come across crystals that do appear to have an iridescence spot on them, the texture appears smooth whereas the texture of most of the colors in question appear grainy. The USGS said that there is also a very high amount of aluminum detected in this stone, I'm not sure if that could have anything to do with any of this but when I looked at a piece of aluminum up close, I do see the colors and texture that I see in the photos. I don't have a clue as to where I found this stone, it's just something that I picked up during my travels in the U.S. Navy, my best guess would be somewhere in California.