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Techniques for Collectorscleaning off the "white stuff" on Milpillas Brochantities

22nd Dec 2015 01:49 UTCbob kerr

I acquired a number of brochantites from Milpillas MX that are heavily coated with "white stuff". thinking first that it may be kaolinite (a clay) I put a specimen in warm/hot water for almost two days. some white stuff came off but there is still lots remaining (see photo) - and probing with a toothpick, I came to the conclusion that it is pretty hard and must be something else - dickite??

any thoughts as to what this may be and what if anything can be done to remove it without impacting the brochantite?

thanks,

bob

22nd Dec 2015 02:37 UTCKeith Compton 🌟 Manager

Hi

I believe that you will find that the white material is Dickite.

This is probably only removable with something like HF acid but then that would also destroy the Brochantite.

I think that unless you can soak it with water and gently pick and remove it with something like a dental probe then I don't think that you will have much success.

Still a nice piece

Cheers

22nd Dec 2015 02:46 UTCBob Harman

Not knowing too much about these minerals, I will start very simple.

Brochantite is a copper sulfate mineral. The white stuff, I do not know, but I might first try vinegar (or very dilute HCl) as carbonates are so common and it should not affect the brochantite.

After the vinegar treatment, whether it has any effect or none at all, I might try a hi pressure cleaning gun. Start off with a very gentle spray in a corner of the specimen to see if the brochantite xtals will stand up to the spray. Only then gradually turn the spray nozzle up to put more pressure into the water stream, seeing if the xtals are stout enough to withstand the increasing spray.

If you are lucky, perhaps much of the white stuff will be loosened and removed. If not, and it remains intact, then I can't help you. Someone else will have more ideas. CHEERS.....BOB

22nd Dec 2015 04:36 UTCbob kerr

thanks kieth and bob - I will break off a small piece of the white stuff and place it in some vinegar and let you know what happens. (need to get some vinegar first!)

the reason i'm leaning towards dickite - which is not a carbonate - is that there are quite a few examples of azurite on dickite from the mine - see photo below - and it really is nice with the azurites as the contrast makes the azurites stand out.

seems that the brochantites are kinda "smothered" by the dickite so it detracts.

other thoughts are welcome

22nd Dec 2015 05:04 UTCDoug Daniels

I would not use any acid with brochantite present... I would think any kind of chemical treatment may harm the brochantite. As far as pressure washing and dental picks (etc), these may work, but you will end up with a specimen obviously treated (especially with the use of picks). Not to mention the possibility of damaging the crystals, or knocking them out of the specimen. In my opinion, I'd leave the white stuff - it is how the mineral formed, it tells more of what happened during/after formation, and you risk destroying the specimen by trying to remove it. Again my opinion(s).

22nd Dec 2015 08:17 UTCDale Foster Manager

Just a personal opinion, but based on the photograph of your specimen I don't think the material detracts from it.

To my mind it is part of the paragenesis for that material, unlike specimens I have collected of tin ore in Cornwall which is covered in dump growth iron oxides that are post mining and are seriously unattractive and benefit greatly from cleaning.

I would personally not do anything to your specimen as I think the risk of damage outweighs any potential gain.

22nd Dec 2015 09:41 UTCDavid Von Bargen Manager

If there are organics holding the clay together, there are a number of chemicals that can be tried (this is something that needs to be tested on a small scale first)

http://soil-environment.blogspot.com/2010/04/hydrogen-peroxide-is-not-good-reagent.html

22nd Dec 2015 13:37 UTCRonnie Van Dommelen 🌟 Manager

I have never tried this but read once about using high strength hydrogen peroxide on clay minerals. The edges and surface area of the clay leads to accelerated bubble formation, causing it to break up.

22nd Dec 2015 15:51 UTCSteve Hardinger 🌟 Expert

I've had some good luck using extended ultrasonic treatment to reduce 'the white stuff' (which I believe is dickite). This treatment has been successful with azurites (on and off matrix) and brochantites (mostly single crystals and small clusters), although I haven't tried on any really spiky brochantite matrix pieces.

23rd Dec 2015 03:26 UTCbob kerr

thank you all for the thoughts - I think I will try the ultra sonic next on the least valuable piece. need to line up an ultra sound machine.

to those of you who think it is fine as-is - I tend to agree and will be keeping a good specimen with this coating in my collection - it is mineralogically interesting - but for the others I think they will be much easier to sell without the dickite - or at least minimal dickite. do a search on minfind and look at the prices these are demanding - but none with dickite coating. this mine has produced the world's best - by far - brochantites and prices reflect this. will report back with results - when I can get to it.

thanks to all,

bob

5th Jan 2016 00:34 UTCDr. Brendan O'Connor

Bob the white material is dickite as a few people suggested and it's a pain in the butt to clean off as you probably discovered. So far I have not heard of anyone having good success at cleaning it off these specimens. These came out early on, back in 2012-13. Aside from some serious manual labor chipping away at the loose stuff you might be stuck with them as they are. I agree that they don't take away from the piece very much at all. I've seen some that are almost totally covered which might be a bit less desirable of course. Fortunately the stuff which is currently coming out if dickite free as were many of the other brochantite pockets in recent years. Good luck and if you do figure out a magic fix do post it!

5th Jan 2016 13:37 UTCReiner Mielke Expert

I think it looks fine just the way it is. The dickite provides a nice contrast, reminds me of plants poking up through the snow.

15th Jan 2016 21:53 UTCbob kerr

got the analysis back - the white stuff is a combo of quartz and alunite - KAl3(SO4)2(OH)6 - (or dickite - a member of the kaolinite group) - so, it appears the specimens stay as they are. like I mentioned previously, I think they are fine the way they are but the market may think otherwise.

thanks for all the feedback

bob

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