FMF - Friends of Minerals Forum, discussion and message board

[Jordi Fabre]

[Peter Lemkin]

[James Catmur]

- Barite, La Unión, Murcia, Spain / white -> blue

[Jose Angel Carrero]

Dear all,
I am an amateur collector from Madrid and a regular FMF user. I recently published a post about the condition of a piece in my collection (Coquimbita on Copiapita), the photos of which I share here.
My interest was to identify the causes of this dramatic color change (see photos). I received some responses (especially from James Catmur, thanks again), indicating that the most likely cause would be the light sensitivity of these minerals. At the same time, he shared links to this long thread from FMF UK (Light Sensitivity of Minerals), which in turn referenced a discussion forum on MINDAT.
MINDAT also referenced a document from The Russell Society, which offered a list of Light Sensitive Minerals, with two sections: Light Sensitive Minerals (color changes, no risk of decomposition) and Sensitive Minerals, with risk of decomposition.
By analyzing the posts on FMF and MINDAT in considerable detail, and by reviewing a List of Sensitive Minerals published on FMF UK and shared on MINDAT, in addition to the Russell Society document, I have compiled a complete list of the minerals referenced there, containing those classified as "A" (there is general agreement to consider the minerals on that list as "Sensitive") and "B" (cases of minerals where there is discussion regarding their sensitivity, including specific cases of sensitive minerals only in certain localities, etc.), and adding information on specific mentions, localities, etc., from the Russell Society report, and especially adding cases of minerals at risk of decomposition "in oxygen".
The current status of the list would require review by experts, such as those of you who are members of this forum, since I am an amateur collector with no special training in mineralogy or geology.
Therefore, hoping you find it interesting, the document (Microsoft Excel, PDF) should be reviewed, which I would email to the volunteer(s) to make the appropriate corrections. Subsequently, we will agree on the best format for publishing the list on FMF UK (and maybe to reference it in MINDAT), and then translate it into Spanish for publication on FMF Spain.
If you find it interesting, please provide me with the email address(es) so I can share the current document.
I look forward to hearing from you.

[Jose Angel Carrero]

Correction: Instead of "FMF UK", it should be understood as "FMF - English Site"
Sorry.

[alfredo]

José Angel, In the case of your coquimbite turning brown, it is not the light but rather the dryness that is the problem. Coquimbite is only stable at atmospheric humidities between 30 < 70 %. Drier, it loses water; damper, it decomposes to brown oxyhydroxides and acid. Drying is reversible by moving to a more humid environment, with recuperation of the original color. If altered by too high humidity then that's irreversible.

[Roger Warin]

Thanks, Alfredo,
You're right, all that crystallization water can never go back into the crystal lattice.
9 H₂O!

[Jose Angel Carrero]

First of all, thank you very much for your quick response.

I'd like to clarify that when I say "dry," I'm referring to an environment where, according to a thermometer I have in the room where I keep the display cases, which measures both ambient temperature and humidity, the average values ​​are between 19 and 21°C, and the humidity is between 40 and 60%.

But... on the other hand, I did a drastic test: I submerged the piece in water for 5 minutes, rinsed it with tap water, and the result is that, as you can see in the photo, the coquimbita has regained its violet color! The accompanying copiapita has regained a lighter yellow hue, but without regaining its shine.

In other words, "Chapeau" Mr. Alfredo.

With this result, I will remove Coquimbita and Copiapita from my list.

And returning to this topic, I would like to reiterate my proposal that this list be reviewed by experts, following the threads opened both here and on MINDAT, and later I would translate it into Spanish for publication on FMF Spanish. To do so, you can send me a PM with your email address so I can send it to you.
Alternatively, I could publish it here, in JPG format, and any forum user could make any comments they deem appropriate, and I would then modify the list.

I remain at your disposal to decide how we proceed.
Best regards.