Cleaning agates that aren’t good for tumbling

[raindropsroses]

hello!  I’m new here and have been tumbling rocks for about a year or so.
I get a lot of agates from the river that look like this and I’m wondering if there is a way to get all the “dirt” crust off out of all the little pits?  It’s not dirt obviously it doesn’t wash off.  
thanks!

[Mark K]

If you want it off, you will have to grind it off. Or cut.

[chris1956]

Welcome from Missouri.  You get a gold star for including pictures on your first post.  

[pebblesky]

Since you already have a tumbler, why don't you want to tumble the dirty crust off? Is it because you still want to keep the bumpy surface, but with that brown translucent color only?

[vegasjames]

Welcome from Southern Nevada.

[raindropsroses]

I’d have to take way too much material off in the tumbler to get the surface smoothed off. I was just hoping there was some acid or cleaner that would remove the crust.

[rockbrain]

It depends on what the crust is made from. I've gotten a lot of rocks from a place nearby to me called Area 54. There is a crust on a lot of the rocks there. It's almost impossible to get off without acid. I dilute swimming pool acid (muriatic) with water, soak the rocks for a while, neutralize with baking soda and water, and rinse them off. Acid will eat away some rocks so be aware of that. I don't think these would be a problem. Working with acid can be inherently dangerous. Take precautions; protective clothes and goggles etc. If you've not worked with it before do some studying first. There's several safety factors to be aware of and an acid burn can be nasty.
Some cooling looking rock you've found. From the pics, I would probably classify it as chalcedony, basically the same as agate but without fortifications, tubes, moss, etc. There are varying definitions though of what an agate actually is.

[raindropsroses]

Thanks! I will give that a try. When you say “a while” do you mean a few hours or days?

[rockbrain]

Aug 14, 2024 18:31:35 GMT -5 raindropsroses said:

Thanks! I will give that a try. When you say “a while” do you mean a few hours or days?

Yes!  I've been very  unscientific with it.  Diluted the acid and unknown amount and then check on them every so often.  The stuff I was cleaning off wasn't host rock.  It's some kind of coating that get's on them later.  It's very concrete like.  Some I've left overnight but they had a thick coating.  Others have just a bit, but it was the only way I was able to  clean them.  I tried pressure washing and a rotary wire brush on an angle grinder.

[stefan]

Cut it off. Get yourself a decent tile saw and cut it off.

[wanderingrockhound]

I know late reply, but my rock problems often sit around a long time: but simple undiluted vinegar will work if its a calcium crust (no need to source or deal with the hazard of muriatic acid), which is very common in my area. Vinegar for a week will take off a very thick crust. If it is softer than the host rockyou could tumble with very coarse sand (#16 grit graded cruhsed quartz) which might work, or use an electirc toothbrush, or a steel wire brush. Need to find out how hard the crust is.

However, the agates I find often have a natural rind on them that is silica but like a bleached zone from the aeons of time its been sitting around, or from when it was made. That is what it looks like to mefrom your picture. I embrace white edges as a part of the rock.

[saaz]

If you're willing to risk a few of them with a test, try tumbling some for a week with only water, no grit. I posted about this experiment a few weeks ago, so you could look up that post. It got rocks very clean without altering the shape too much. Softer rocks that are mixed with harder can come out hazy, similar to a normal coarse stage, but harder rocks actually shine up a little.

[ronnsrockroundup]

Aug 16, 2024 15:49:45 GMT -5 stefan said:

Cut it off. Get yourself a decent tile saw and cut it off.

Yep.