Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

Techniques for CollectorsPLEASE HELP!! My telluride is black!!

19th Apr 2016 22:16 UTCAurum Williamson

Hi Everyone,

I think I screwed up bad. I have a specimen of sylvanite on quartz crystals and matrix. The specimen had an iron oxide coating on everything dulling the specimen. I got a wise idea that using some oxalic acid to remove the iron staining was the way to go. Well within a few minutes the whole specimen turned black. I've never seen this. I could see a chemical reaction with the sylvanite happening, but the quartz and matrix also turned black. This is odd. Do you thing the specimen had been coated with something and the oxalic acid reacted with it? I really need to clean this specimen. I don’t want to concede to my stupidity.

Thanks for your help,

Keith

19th Apr 2016 22:44 UTCBob Harman

Maybe I am not familiar, but I thought TELLURIDE was a small ski town in Colorado with a colorful mining past. Is it also a mineral?

So as an addendum, I did some further reading and tellurium can form compounds with silver and gold. The minerals formed include sylvanite (mentioned by the poster) and the related mineral calaverite. I knew that, but these may correctly be called silver gold tellurides so I guess you might actually say that "your telluride is black". In any case I see where reactions with reducing agents and acids can create other compounds and complex tellurium organic gases as byproducts. Anyway, learn something new everyday! CHEERS.....BOB

20th Apr 2016 00:00 UTCPavel Kartashov Manager

Next time you will use EDTA for cleaning.

20th Apr 2016 07:20 UTCReinhardt van Vuuren

Pavel WTF is EDTA? :-D

Keith don't feel bad I am sure everyone that has worked with acid has at some time or another destroyed a specimen in the process, its what you learn from it that is important. I once ruined a palm sized azurite possibly from Tumeb with vinigar, this was one of the first things I've ever treated with acid, lessons were learned, then I moved up in the world and cleaned a prehnite with HCI only to discover that this thing was 50% calcite and the prehnite is crumbly with a big air pocked between it and the base/matrix, then I moved up in the world wanted to use HF hydorflouric acid to clean another prehnite but couldn't find any locally so I found glass etching paste at the local craft shop well it cleaned it nicely but it mats everything it touches so I ended up with a mat prehnite, some olive oil got rubbed into that piece, still smells funny. So you are not alone my friend. (tu)

20th Apr 2016 07:34 UTCAlfredo Petrov Manager

Reinhardt: EDTA = Ethylenediaminetetraacetic acid, a relatively non-toxic acid that is even used in foods, medicines and cosmetics. Excellent at chelating Fe (and some other metals).

20th Apr 2016 10:58 UTCReinhardt van Vuuren

Awesome, thanks Alfredo (tu)

20th Apr 2016 13:05 UTCPavel Kartashov Manager

EDTA isn't acid, but is its Na salt. EDTA is neutral (pH~7) reagent. You may even to drink its solution. By the way, it using for sober up of alcoholics in some clinics. Of course EDTA for ingestion must be chemical pure, not technical.

Search EDTA on eBay. In Russia this reagent known as "Трилон-Б".

Note that EDTA dissolves carbonates - for example dolomite is soluble in it better than in concentrated HCl.

In difference from oxalic acid EDTA don't leave after it insoluble products of reaction similar to Fe[C₂O₄]*2H₂O.

Probably it will be able to clean up your specimen. At least quartz of it.

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 26, 2024 22:31:31

Go to top of page