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Techniques for CollectorsUraninite in Matrix

11th Sep 2009 03:56 UTCAndrew Johns

Hello, I have a cubed Uraninite in Calcite matrix in which I would like to expose more of the cube. Will Muriatic Acid damage the Uraninite crystal or is it safer to use Acetic?? Or should I just leave it alone??

Andrew Johns..

12th Sep 2009 04:07 UTCMichael J. Bainbridge Expert

I used HCl to etch out some molybdenite in calcite from the Chaput-Payne property in Quebec and, much to my surprise, there was a uraninite octahedron perched on the edge of one piece. That has been my only experience with uraninite in HCl, but it came out beautifully - quite lustrous. I would recommend leaving some of the matrix though, as they can sometimes be fractured an might fall apart if you etch it out completely. Besides, they usually look better that way anyway.

Good luck!

13th Sep 2009 19:38 UTCAndrew Johns

Thanks Michael, I do want to leave it in Matrix, just want to expose more of the cube is all.

Andrew..

14th Sep 2009 03:41 UTCTim Jokela Jr

Dilute HCl will do fine, but watch it like a hawk or she'll pop off.

T

14th Sep 2009 04:32 UTCAndrew Johns

Thanks for the tip Tim,will watch it carefully. Hope to see you maybe in the fall at Montrose Occurence if we all can organize a day.

Andrew.

14th Sep 2009 07:59 UTCMatt Neuzil Expert

I am not sure what your HCL is but i think mine is like 33% you can always dilute it more.

I believe the correct way to do this is start with your container/bucket of water and add the HCL to the water. I could be wrong, please correct me if i am. but this could also help you in monitoring more closely how fast your calcite dissolves

14th Sep 2009 15:02 UTCMichael J. Bainbridge Expert

I take the over the counter muriatic or HLC (depending on where you buy it) and dilute it to 20%. The easy way to do that is to take an empty 4l bottle and put in 3l of water (12 cups) and draw a line. Then put 750ml (3 cups) more in and draw another line. Then when you're ready to do some etching, fill to the first line with water, then to the second with acid. Instant 20%. Pour that into the bucket with the specimens and repeat until they're covered.

You can use 25% (3l water, 1l acid) if you're in a hurry, but I wouldn't exceed that as it can take the some of the luster off certain "safe" minerals like diopside if it's any stronger. If you really want to be careful 10 or 15% is good. Even at that strength it will still do a number on apatite though so make sure there's nothing like that you want to save.

Happy bubbling,

Michael

14th Sep 2009 15:25 UTCMichael J. Bainbridge Expert

I just checked the bottle and it's the same concentration as Matt's (33%), so I guess that means my 20% solution is actually 6.6%. In my experience that's plenty strong enough though. Just about the right speed too. You can easily leave it unattended for an hour or so without loosing too much matrix, but a couple more of baths of that will usually finish the job (depending, of course, on how much calcite you're starting with). In the past I have tried solutions as strong as 50% of the over the counter strength (16.5%, I guess) and it has taken the shine off of even some amphiboles.

I guess it just depends how patient you are. Do some experimenting but err on the side of caution.

Michael

14th Sep 2009 17:24 UTCDonald Vaughn

since we are talking about diluting acid always remember the old saying "do as you otter, add acid to water" nasty things happen when you add water to acid especially concentrated acids can be quite spectacular as well as quite dangerous; "safety first"

14th Sep 2009 18:11 UTCDon Swenson

Use dilute HCl & be vigilant. If the uraninite is oxidized, attack this problem with iron out.

15th Sep 2009 01:07 UTCMaggie Wilson Expert

To add to Don's comments about the uraninite being oxidized - if the crystal is oxidized, any cracks will be more evident once the acid has cleared the oxidized bits.

15th Sep 2009 01:47 UTCAndrew Johns

Thanks everyone, I usually dilute it 10:1 when removing Calcite. I'll dilute a bit and then use a glass eyedropper to just remove enough calcite to expose more of the Uraninite. As always I add acid to water, work outdoors and use safety eyewear and gloves. You can never be TOO careful. I want both eyes to look at my specimens.

Andrew..

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