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Techniques for Collectorsextracting limonite crystals from rock

27th Jun 2017 15:46 UTCDaniel Bennett

breaking the rock with a hammer is works about 50% of the time. they pop out. but its sad the other 50% when the crystal breaks in half and they are not all that abundant in the first place. will acid do the trick or will it destroy the crystal? I thought about boiling the rock and freezing it a few times to maybe break it down. or heating it in fire and dropping in water. I don't have that much material to experiment too much so any suggestions will be appreciated.

27th Jun 2017 16:11 UTCReiner Mielke Expert

I presume you mean limonite pseudomorphs of pyrite in schist? If so then as far as I know "hit-and-hope" is the only way.

27th Jun 2017 16:12 UTCKevin Conroy Manager

This may help: http://www.rockhoundingar.com/trimming.php


I would definitely recommend getting a rock trimmer if you're going to be working on a lot of delicate specimens, or if you want more control over where the rock breaks.

27th Jun 2017 16:19 UTCBob Harman

I thought "limonite" was older terminology for an amorphous NON-CRYSTALLINE earthy brown mixture of iron oxides. Please correct me if I am wrong.

In Indiana this is often seen as iron rich (ferroan) dolomite corrodes into the amorphus limonite mass. After soaking, I use a hi pressure cleaning gun to help remove this stuff.

CHEERS.......BOB

27th Jun 2017 16:51 UTCTed Hadley

Rock trimmers are available from Swarf Systems www.SwarfSystems.com

27th Jun 2017 17:47 UTCDon Saathoff Expert

Hi Daniel,


It seems that we are not sure what you are talking about. As Bob said limonite is a mixture of iron oxides/hydroxides and tends to form as a product of the weathering or "breakdown" of another iron mineral. If your crystals are cubes, the limonite has probably replaced pyrite. If they are pyramidal it has replaced magnetite or chalcopyrite or, again, pyrite - or any of many iron minerals. If you could add a clear picture of the specimen we would have a better understanding of what you are dealing with and would be more likely able to help.


Don S.

27th Jun 2017 18:17 UTCMatt Courville

I've tried to trim down rocks with these and I would think that it has less to do with the techniques(hot/cold) and more to do with how the crystals/host rock was formed (which I would guess will fracture the same way whether hammer or temp.). I had an ugly oversized chunk with some nice small cubes and never wanted to risk trimming it down since they were all tucked into a crevice and would likely bust apart when trimming. It sat in my shed un-appreciated for a year until just about 3 weeks ago I tried to see what could be done.....lost them all.


Daniel, I would try practicing trimming on junk rocks more than temperature techniques, other than buying a rock trimmer. Acid only works with particular things such as garnet, epidote, in calcite etc. Some use saws to trim-down, but many don't like this and feel that it makes the piece loose value. If you don't mind, this could also be an option at a local club if you don't care to buy them yourself.

27th Jun 2017 19:01 UTCWayne Corwin

Daniel, we really need a photo if you want some help.

28th Jun 2017 01:59 UTCDaniel Bennett

02513680016034718765365.jpg
here is an example of the rock. Phyllite . I've broken up several of these.





these next two pictures are one piece that I'm done hitting with a hammer.the crystals might be attached to each other.


05145830015653102528563.jpg



I glued the corner back on.
06253730015653102525137.jpg



I have a pile of broken rock that might have more crystals inside if I had a way to dissolve the rock. how to speed up the natural process of breaking it down.

28th Jun 2017 02:15 UTCDaniel Bennett

08495450016034718767993.jpg
I got lucky these ones didn't break.



this one would pop right out but I wont.
08016800015653102526724.jpg

28th Jun 2017 05:00 UTCGregg Little 🌟

Very poor grade of phyllite as the schistosity or foliation appears quite week. The bottom picture (736) even looks like a siltstone or very fine grained sandstone and the break almost looks "conchoidal", certainly brittle. Nothing will dissolve the rock and leave the pseudomorph intact. I imagine the trick to trimming is to know when to stop.

28th Jun 2017 06:02 UTCDaniel Bennett

that picture doesn't show the foliation that much. While searching for it in the field I definitely noticed it occurs in a green, wavy , banded sedimentary rock with a sheen almost chatoyant quality. which matchs the phyllite description I read in my rock book. the reason I looked it up was I heard of another nearby occurrence of limonite crystals in phyllite.

I might trim 736 flat on one side so it will stand and display the crystal. what can be done with 744?

28th Jun 2017 06:06 UTCDavid Sheumack

Daniel, perhaps using an air scribe might be of benefit to expose these crystals with minimal damage. This is one supplier in USA, https://www.paleotools.com/which-tool-is-right-for-me

28th Jun 2017 10:27 UTCPeter Nancarrow 🌟 Expert

03213940016015722344365.jpg
The pentagonal dodecahedron is a very characteristic crystal form of pyrite, and it commonly shows parallel striations such as can be seen in your last photo, so it looks like your crystals are (or were) pyrite, which has been oxidised, at least on the surface, to 'limonite'. (Usually goethite, lepidocrocite or some other mixture of hydrated iron oxides)


I would say that the rock matrix doesn't look like the sort of material which would be susceptible to any sort of "heat and chill" technique, which wouldn't be just as likely to fracture the crystals as well, so some sort of mechanical/hydraulic splitting, using something like this:




would probably be the most sucessful way of extracting them.


Having said that, if they were mine, I would keep them with at least some attached matrix (such in your last photo), which has much more geological/mineralogical interest than simply a stand-alone oxidised pyrite crystal.


Pete N.

28th Jun 2017 15:33 UTCDoug Schonewald

Daniel,


The only way to break open the rock and expose crystals is a splitting tool or a hammer and chisel. Using an electric drill with a small carbide bit, and drilling a line of holes, can enable you to break the matrix away exactly where you want it. You are going to lose some crystals, so collect more than you need. Once you break the rock enough to partially expose a crystal you could try an electric engraving tool and use that to carefully chip around the crystals and clean up the drill marks. Another option is a small dremel tool with diamond tools to grind and cut away the matrix to better expose the crystals. I've seen some pretty nice work done with a small trim saw and then chipping away the saw marks with an engraving pencil. The result was a nearly invisible cut line and a fine specimen. It is very time consuming and labor intensive, and may not be worth it commercially, but it will give you some very nice specimens for your personal collection or to give as gifts to friends.


Doug

28th Jun 2017 17:45 UTCScott Rider

My question is why trim 736, matrix specimens can be interesting. I can understand why you want to break up the others, as the pyrite pseudo's aren't well displayed, but on the last image, you should leave that one alone. Its kind of cool that it is still on the matrix. I personally would like it on matrix vs. the crystals being removed.


If you are trying to sell them, then leave 736 alone. It may sell better being on a matrix. People like that, as it can make displaying it easier, and its more interesting to really serious collectors whom are more interested in pieces on matrix than being loose.

29th Jun 2017 19:21 UTCDaniel Bennett

02200270016034718777125.jpg
you guys hit the nail on the head. I found my old tool engraver. it worked like a charm. those crystals are tougher than I thought. I was able to hammer away directly down on the crystal with no damage whatsoever. now I want to try an air scribe. that trimmer looks pretty sweet as well.


here is an after picture of 744/745.



it looks like it was a single crystal that broke. any guesses on when this occurred? at the time of rock formation or later on during some seismic event?
09963950015653102529178.jpg



this is the engraver.
01048490015653102537522.jpg



thanks so much for the good responses.

29th Jun 2017 19:41 UTCDaniel Bennett

04210900016034718775040.jpg
Scott I agree with what your saying. I thought just cutting a flat spot so it stands up nicely.




I also want to show how cool they look on there own. with no work. these were loose in the gravel.





a before and after using the engraver
02078380015653102531982.jpg

03355900015653102537012.jpg


thanks again

29th Jun 2017 20:10 UTCMatt Courville

Depending on the piece and the alteration, 'Super Iron-Out' can give some dirty pyrites a neat clean finish. I would be tempted to try a few to see what the outcome is. Post a photo if you try this;)

29th Jun 2017 23:54 UTCScott Rider

Matt has a good idea with the Super Iron-Out. I have not thought of doing that on some of my pyrite that has the oxidation (or the pseudo's either)... Just don't leave them in the Iron-Out for too long... How long...? I would not know, but you seem to be adapt at experimenting. I assume it'll depend on how deep the oxidization goes into the crystals...


However, I would do the tests on damaged, ugly ones if you have any first, just in case it doesn't turn out the way you wanted.

10th Mar 2019 00:37 UTCEd McKay

I have hundreds of these on my property in southern PA. ,many contain pyrite,Sizes vary from quarter inch to 4 inch cubes.Also many contain twins embedded.

10th Mar 2019 01:54 UTCKevin Conroy Manager

Ed, please provide some photos!

13th Mar 2019 00:47 UTCEd McKay

08004190016034718789491.jpg
This piece of limoniye is my 3rd largest it is 1 1/2 inches square.I have a large Basket full of these,Thanks

04781120015653102537148.jpg

13th Mar 2019 00:50 UTCDoug Daniels

Not too shabby for Pensylvaynee (yeh, I lived there for two years....).

13th Mar 2019 23:32 UTCEd McKay

01023630016034718798894.jpg
Here is two photos of my limonite,Broken pieces,these 2 do not have gold colored pyrite,Why I am not sure,they contain silver toned crystals.I also have some green colored sand that i collected in an ultra-mafic formation,serpentine rock barren.Known as Bare hills,once a chrome mine and copper mine existed there.This crystal green sand leaches out between fissures in the serpentine rock.Would like to have it identified!Where on mindat do I post photos of it. THANKS

05354550015653102537129.jpg

17th Mar 2019 21:49 UTCEd McKay

I went to Mineral hill mine today,in Maryland.Collected specimens of Pyrite,Chalcopyrite,asbestos and Goethite.There are tons of sulfides and iron ores there.Many open pits and two mine dumps.In previous trips there I found native copper,Malachite,Chalcocite,Bornite,Small amounts of Stannite,large amounts of epidote as well as Talc.Well worth the trip I live 30 miles from there.I have been going there since 1980.Anyone interested in going there contact me If you need help finding it. https://www.mindat.org/loc-16392.html
 
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