FMF - Friends of Minerals Forum, discussion and message board

[Charly H]

Hi I am pretty new to all this, came upon this enormous piece of what I think is tremolite/actinolite (but open to other suggestions) at an auction, I do not have a location for it. Is there any way to remove that corrosion and tarnish from the outer weather rind? Is that even a thing eight this mineral? Or has this one been damaged/altered beyond saving? I have some experience using iron out and other mild acids but nothing major. Thank you for your help!

[alfredo]

Seems likely that the yellowish brown crust is iron oxides, so a bath in either Iron Out or hydrochloric acid (neither of which will hurt tremolite-actinolite) should help, followed by some scrubbing to remove clays. If using hydrochloric acid, the piece will need a second bath in citric or phosphoric acids to prevent unsightly stains.

[Charly H]

Thank you for your help, I will give it a go. I tried scrubbing but it just started to damage the specimen because the outer weather rind is very soft and brittle. I’m a little concerned about toxicity, too. What would cause this to become so corroded? Is it natural or from poor storage like pyrite rot? Thank you again.

[alfredo]

Some iron minerals must have decomposed and oxidized at some point, but hard to say what they were; lots of possibilities: sulphides probably the most likely (pyrite, pyrrhotite, etc), carbonates (siderite, iron-rich dolomite, etc), even other silicates (biotite...). Unlikely to be anything toxic left in the rock, just in the chemicals you use for cleaning it; so use rubber gloves, and rinse well.

[Pete Modreski]

Charly, some rocks are just dirty and weathered enough, and have enough insoluble mineral crusts on them, that they are either just impossible to clean, or would require such repeated and "exotic" chemical soaking and cleaning treatments, that it is not worth the trouble. You tremolite-etc. rock specimen likely falls into this category (sorry to say). Unless it is really, really special to you!

If the specimen were something with crystals (like quartz) that had smooth, clean, hard crystal faces (underneath all the surface weathering deposits), it might be more amenable to eventual cleaning to a "pristine" state. But tremolite, with its fibrous/platy nature and strong cleavage, having so many cracks/fractures in which "dirt" and weathered deposits (plus perhaps algae/moss, etc.) can penetrate, well, there's probably less hope.

[Matt_Zukowski]

Maybe you wouldn't want to do this but if this was my rock i'd hit it with a hammer and see what was inside. Maybe you'll find something nicer you'd want to keep. If not, it will probably be because it is just too weathered, and not worth dealing with. Just my opinion.

[Charly H]

I figured as much but it was worth asking, thanks for the advice! I am now tempted to crack the sucker open, what is the best way to do that? Dead blow hammer and a chisel? Would I have to worry about toxic particulate in that endeavor? My fear is that it will kind of just chip apart in minuscule pieces. It’s very brittle!

[James Catmur]

Do you have a press or jack you can use to slowly squeeze a wedge into it?

[Charly H]

I got a hydraulic press and a chisel! What could go wrong?!

[Matt_Zukowski]

Yes indeed.

[James Catmur]

Just do it slowly so it slits gently. See what you then find