FMF - Friends of Minerals Forum, discussion and message board

[Pete Richards]

I have several cubanite crystals from the Henderson #2 mine in Chibougamou, Quebec, Canada. I have had them for between 23 and 35 years. Recently I noticed that they are all tarnished blue-black. They are in plastic thumbnail boxes, displayed on Styrofoam, held in place by a standard grey mineral tack. They have spent most of their lives with me in wooden cases, including oak, birch, and poplar woods at least. Our environment in Ohio is temperate and moderately humid.

Can anyone provide insights into the alteration of cubanite in collections? Might any of the organic materials around them be contributing to their tarnish? What is the best way to brighten them back up again – or should I not do so at all?

Any and all thoughts welcome!

[Roger Warin]

Hello Pete,
I give my limited impressions of this exceptional mineral.
Thank you for putting the cubanite on top of the pile of my questions.
At room temperature, I thought the cubanite was stable.
But we must remember its origin in high temperature hydrothermal mineral deposits with pyrrhotite Fe1−xS (x = 0 to 0.2) and pentlandite (Fe,Ni)9S8. This one is often included in pyrrhotite.
Nickel is a frequent impurity of iron (nucleosynthesis).
However, there is another similar mineral, chalcopyrite. A fortiori that cubanite and chalcopyrite form a solid solution at high temperature.
Therefore, at room temperatures one can find some intergrowths with chalcopyrite as exsolutions of this solid solution.

On this subject, I have never understood why terrestrial pyrrotite does not exist in meteorites, where only stoichiometric FeS troilite is found.
Conversely, troilite does not exist on Earth!

In my opinion, a slight deposit of pyrrhotite may be responsible for the visual alteration of your samples.
I will be wary of any chemical attack on these minerals. Maybe a very soft nail brush used by manicurists!


Fortunately, I have a sample of cubanite from the same period (June 1992). It seems correct to me. It has been in this platic box (Jousy) for more than 30 years.
When the light of day will be there, I will take some pictures.

[Philippe Durand]

My old pyrites had a tarnish with time

I have cleaned them with that:
https://www.amazon.fr/pierre-dargile/s?k=pierre+d%27argile
(link normalized by FMF)

you may have the same type of product

it is a clay used to clean ceramics.
I have rubbed the crystals lightly with this product and a bit of wet, then a wash of alcohol and a smooth dry, and my pyrites shines again

may be you can try on the back side of one crystal

[Jordi Fabre]

[bob kerr]

i would bet that Simple Green will do wonders on there and wouldn't hurt them even if it doesn't remove the tarnish. Sulfides respond well to this cleaner and as Rock Currier used to say - every ton of sulfides from Peru have been cleaned with Simple Green - especially pyrites and cubanite is very close to iron sulfide.

bob

[Joseph DOliveira]

I use a kitchen cleaning product call VIM cream cleaner (NOT the abrasive VIM powder cleaner) with a soft toothbrush, that will probably work at removing the tarnish and restoring the luster. It works well on pyrite and chalcopyrite, should be fine for your cubanite. Always safe to try it on a less expensive piece first.

[lluis]

Dear all

What you are talking about are polishers (I wonder if they are micro silicon dioxide(quartz...when big), or aluminum oxide or anything else.
Yes, they work w¡very well...but they let scratches (not visible at naked eye, but yes under microscope)

Maybe trying a complexant, that takes the iron in the tarnish would work same, and surface could look etched under a potent microscope, but not scratched....

I am wondering in the phosphonates series... Common in textile, but no idea how easy to find it is in your countries (If you have a friend in any textile finishing company, easy. If not.....)

With best wishes

Lluís

[Jordi Fabre]

Take care with the Cubanite. Unlike other sulfides, the Cubanite reacts poorly to any type of cleaning. In the short term, it may appear to have been cleaned, but it usually reappears the tarnish in a short time, and sometimes this darkening is even darker and harder to clean.

[Roger Warin]

Hello
The relief of the crystal is too important to take an abrasive.
An iron-specific complexing agent would be effective.
Here is my crystal (collected in 1992).
He is flawless.
Here are the macro photos.

[Roger Warin]

Hello,
Here are binocular shots.
The direction of the rays reflected off the optical axis are almost black.
The sequence of photos shows the end of the twin which is built step by step, stitch by stitch, like a knit!
The cubanite is not altered, without special precautions.