FMF - Friends of Minerals Forum, discussion and message board

[Turbo]

I have this fluorite from the Okoruso Mine, Namibia. It has a frosted appearance that hides its beautiful internal characteristics. Is this frosted appearance natural, or is it the result of some sort of chemical cleaning that occurred before it was sold? As you can see in the picture, there are some reddish areas between some of the crystals that leads me to believe that there may have been a kind of coating on this mineral that was cleaned away.

What do you guys and gals think?

Are there ways to polish up the faces of the crystals to recover some of the beauty? If this is a natural fluorite, I'm uncomfortable with polishing it, but if it has already been etched by chemicals, I'd like to recover the shine, if possible.

Thanks

[Jesse Fisher]

Unfortunately, it is difficult to say whether the delustered finish on the fluorite is natural or induced by some attempt at chemical cleaning based on one low resolution photo. If someone used oxalic acid to remove iron staining from the specimen, this would certainly have etched the surface of the fluorite. However, it is not impossible that a final coating of some secondary mineral such as quartz or iron oxides had intergrown with the surface of the fluorite, and when removed with something that will not harm the fluorite (such as sodium dithionite or HF), left a slightly pitted surface. Regardless, perhaps the only thing you can do that will improve the specimen's appearance at this point is to give it a light coating of either mineral oil or silicone.

[Peter Megaw]

Turbo, these comments are intended to cover your situation, but also for any "how do I clean this dull looking specimen" situation. As always, I recommend you check out the cleaning advice in Sinkankas's "Gemstone and Mineral Databook" as well as the chemical handliing cautions therein.

First make sure the crystals are truly frosted and not just coated with a microfilm of silica or other species not likely to have been dissolved by whatever was used to remove the iron oxides. (it is possible that the faces were never truly lustrous and the frosting is revealed to be a natural hackly fluorite surface that you will never improve). A bamboo skewer rubbed gently across an inconspicuous face may tell you quickly if there's good luster hiding beneath. Checking it out under the microscope might help too. If it's an insoluble, but physically removable coating you might try one of the "soft-abrasive" cleansers that use gypsum as their abrasvie agent instead of silica. You'll have to brush each face individually...but this works well on many species in the hardness 2-6 range. Some of these cleansers incorporate bleach, scents or other cleaning "booster" that may cause unwanted patinas or other reactions, so go for the simplest formulation possible.

If a coating is not physically removable you may be getting into the realm of some nasty chemistry. If it's silica you could get it off with HF without too much risk to the fluorite...being careful to fully neutralize the HF afterwards. If you are not familiar with the safety precautions required by HF, get an expert to do it for you.

The iron-oxides do look like remnants from incomplete cleaning, but it would take some pretty stout chemicals to have frosted these fluorites like this. Unless the cleaner went overboard, or left this piece in the "soup" much too long, I suspect the frosting occurred from the same fluids that deposited the oxides in the first place, so is effectively natural. Similar frosting is often seen on calcite after removing iron oxides even with organics such as iron-out.

In either case the crystals are etched and the natural luster is gone for good. Polishing each face would be a tremendously tedious job probably costing far more than the "restored" piece would be worth...leaving you with backlighting it or oiling it (which many justifably consider a no-no).

Since there are many nicely lustrous pieces from Okoruso, once you determine there is no easy solution, put the piece in your sale or trade flat...with a realistic value given its luster-challenged status...and invest the time in earning the money for a new and better specimen.

[Jesse Fisher]

A word of caution about Sinkankas' book - he recommends using oxalic acid to remove ironstaining from fluorite. While oxalic acid will work on many minerals (such as silicates), it will permanently deluster fluorite very quickly. I have mistakenly done this myself, and afterward, there is not much to be done about the condition of the fluorite. I suspect that this may be what was done to your specimen, but hard to say for sure without examining the crystal surfaces with a stereoscope or loupe.

Peter is correct that a micro-coating of silica may also cause this sort of appearance, and that HF will remove it without harming the fluorite. HF, however is an exceedingly dangerous chemical to handle and I discourage anyone who has not had training in laboratory safety and access to professional equipment from trying to use it.

[Peter Megaw]

Another general comment about oxalic...for other applications like getting iron-oxides off quartz. You MUST use demineralized water or you run the risk of depositing insoluble calcium oxalates that are a nightmare to remove...

[Turbo]

I took a look at it through a loupe and it's definitely not a coating. It looks like lots of tiny pits in the surface. It seems like it would be more trouble than it's worth trying to polish them out. I think I'll try mineral oil and see how that looks, but I may have to think about making some better investments. I try to limit spending while trying to get nice specimens at the same time. Sometimes that is hard to do.

[Jesse Fisher]

One of the things any serious mineral collector quickly learns that it is always a good idea to buy the best specimens, even if spending the money hurts. The best quality specimens are the only ones that will stand a chance of paying you back on your investment when time comes to sell, and as a collector, you probably won't satisfied with less than the best you can acquire, anyway.

[Turbo]

I agree. I'm going to save up for a while and look around more carefully before my next purchase.

[Jason]

Thats what we call a Matte finish. The quartz crystals from Diamond Hill mine in South Carolina show this "frosted" apperance. A little trick that helps give matte finish minerals a little shine is this stuff called "Saw Sheen". It's used on granite or to help polish granite or something along those lines. It gives matte finish minerals that wet look and takes away the matte look. Of course, I always recommend leaving minerals as is since I am a purist but if you fancy a more lively or vibrant look that the matte finish doesn't provide then Saw Sheen is the way to go.

[Debbie Woolf]

I can confirm what Peter said about left in the chemicals too long as I have seen with my own eyes what this does to Fluorite from Okorusu at a dealers home in Windhoek, they smell oily to !

[Turbo]

It doesn't smell oily, so the pitting may be natural.

I think I'll be unorthodox and try mineral oil. Maybe at a later date I will experiment with dental polishing discs on a hidden surface. Whatever I decide to do, I'll be sure to post the results.