Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

Techniques for CollectorsAmmonium Bifluoride causing a white precipitant on quartz:

4th Oct 2007 19:11 UTCDane

Does anybody know the condition that causes this, the composition of the precipitant, and recommendations for removing it?

4th Oct 2007 20:31 UTCJesse Fisher Expert

What you are likely seeing is not a percipitate but alteration of the quartz by the free fluoride ions from the solution. Unless you are trying to etch or remove the quartz, it is not a good idea to put it into any solution containing fluoride radicals. The only way to remove this would likely be with an air abrassive unit using glass bead. The quartz is likely to remain pitted and/or delustered.

4th Oct 2007 21:03 UTCdane

I refered to it as a precipitant because i have been able to scratch it off, but with significant force. Additionally it only coats the micro-etched surface of the quartz crystals where nucleation can occur, but not on the smooth surfaces (for the appearant reason).

My interest, of course, is to remove the weaker bonded silicons (clay silicates) that have naturally coated the specimens in their hosting environment, however on an occasion and for reasons currently unknown, a new coating has resulted.

I have attempted to reverse the process based on concentration gradient and a little thermal induction, but no success. If the coating's composition does not contain fluoride, then i may reattempt this with higher temperatures to dissolve the coating.

Any ideas? Thanks

5th Oct 2007 07:31 UTCDane

I attached an image illustrating what i am refering to as a coated specimen (on the left) and a specimen that has been allowed to be overexposed to ammonium bifluoride (on the right) that resulted in a porous-textured alterations along internal fractures.

5th Oct 2007 13:37 UTCAlfredo Petrov Manager

Dane, we need an analysis of your coating to be sure what's going on, but here are two mere guesses:

1) Your bifluoride solution is too old and is getting close to being saturated when warm, so when it cools down (at night perhaps?) it gets saturated and silica precipitates out. Try fresh bifluoride solution.

2) You have some Ca-bearing mineral in there, and fluorite is being precipitated.

And I agree with Jesse that bifluoride can damage ordinary quartz crystals, unless you use it for only a very limited time.

5th Oct 2007 17:17 UTCDane

Alfredo,

Its interesting you say that, 1) was my rationale last week because I was using an old solution to treat some oxalic/hydrochloric-resistant coatings; since an old solution has an affect on this stuff but no longer on clay-silicate coatings. So i created a fesh batch, tested a disposable specimen, and ended up with the worst coating yet (see previous picture).

The only correlation I have yet to make is that has only occured on pegmatite-quartz and not on quartz that i have collected from quartz dikes. Additionally when treating pegmatite quartz, the results have not been consistent with temperature: it can happen during winter temps (45-75F) or not and it can happen during summer temps (65-95F) or not; i am baffled at this variable.

2) is a very good suggestion because the refered quartz dikes are essentially CA free, but the pegmatite sources, i believe otherwise, given the common compositions for pegmatite rocks. It would also explian why the precipitation only takes hours while the alteration of the quartz structure being stripped by free fluoride ions takes days for the same concentration.

The only doubt that i have that its fluorite is that the coating has a hardness greater than metal; then again this could be contributed to micro protrusions of the rough quartz surface (where the fluorite exits in the micro-pits).

Any suggestions for better testing/removing suspected fluorite? I guess i can throw in some calcite when i get home.

7th Oct 2007 05:11 UTCSteve Hardinger 🌟 Expert

The pictures posted previously in this thread suggest (to me at least) that the precipitation phenomenon is not a simple issue. Note that only some (not all) of the quartz faces have been coated.

Beyond that observation, I don't have a clue.

7th Oct 2007 15:51 UTCdane

Thanks for your all's input, it has made me more confident in my observations. Once i return from Gem-o-rama, i will run some more tests.

Steve,

Thank you for responding to my request. Is there a lab you recommend i can send in a coating sample for compositional analysis?

Thanks again,

Dane

5th Nov 2007 17:29 UTCPaul Young

Dane,

By any chance are these quartz's from Sierra Blanca in New Mexico?

I use HF (around 10% solution) to clean my quartz from there and have had the same type of coating which does come off with "refreshed" acid. I have found that I could use a wire brush and remove the coating but the dust is another issue and it takes a fair amount of time plus not all of the coating is removed.

Paul

19th Nov 2007 21:33 UTCdane.balderston

Paul,

I am interested in discussing your observations and recommendations however i restrict myself from discussing specimen origin, including National Forest, on public domain (internet).

If you would like to discuss this further, please do; i have an email @ gmail.com under "Posted by:" you see above.

Talk to ya then,

Dane

29th Mar 2008 12:56 UTCRock Currier Expert

Duane, Such coatings can usually be quickly and rather completely removed with an air abrasive tool using glass beads.

Rock

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 19, 2024 21:30:22

Go to top of page