Lapidaryforum.net
Rock Art => Cabochons, Intarsias, Cameos => Topic started by: Opal Mike on March 26, 2020, 11:18:50 PM
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Hi all,
Since I stopped commercial wholesale production in my opal workshops, I have had a lot of fun sourcing and cutting some different material, mostly Australian rough.
I have always loved Marra Mumba Tiger eye and I have been playing with it for a while now.
I noticed a post that talked about asbestos risk in tiger eye and I thought I would add to it. Firstly I think most of you know that tiger eye is formed by a process that sees the original asbestos fibres replaced by quartz type columns or fine fibres. Most definitions will state that the new ‘tiger eye’ as replacing the older asbestos, is now free of asbestos and safe to cut for us lapidaries.
Felecia is spot on though with her comments, and this is pertaining to the highly sought after Australian Marra Mumba variety. This material varies greatly in hardness, with some material, especially the blue stuff often being more fibrous, and yes clearly containing silky unstable threads of asbestos. It doesn’t end there though. You can find this in the bronze redder material synonymous with Marra Mumba, and indeed some of the yellow and golden coloured material.
Care needs to be taken!
Whilst the majority of this majestic stone is pretty safe to work I would urge all of you to presume the following; it isn’t!
You can work this stuff safely. Make sure you take the steps Felicia adopts by making sure you never grind or sand this material dry...use plenty of water. I would expressly add the following to that; wear a mask at all times, and when you have done with the grinder and sanding stages on your wheels, make sure to clean everything properly and safely. Scrape and bag up the wet sludge residue as built up on and around the machines and trays every day; don’t let the ground residue build up and dry out and potentially tun into breathable dust particles.
I keep my workshops very clean. I mop the floor every day, clean the machines and keep all dust to a minimum....we can all do that whatever our space, and whatever machines we use.
For anyone that thinks asbestos is nothing to worry about, think again. No stone dust is good for us, silicates etc, so get used to keeping things clean, and wear masks all the time.
For those that don’t know what Marra Mumba tiger eye is please keep reading.
The Murra Mumba brand was first established in Western Australia following a deposit of stunning tiger eye found in the 1970’s by Glenn Archer. This material contained the red bronze tiger eye and was mixed with bands of hematite and a variety of stunning jaspers. By definition, Marra Mumba must contain a mix of these colour especially the bronze tiger eye, along with the Jaspers and hematite. The material is simply stunning with amazing chatoyant vibrant colours and patterns, and very different from the more abundant golden banded varieties coming out of Africa.
Tiger eye is notoriously challenging to cut in terms of achieving a nice glossy fine polish, and each stone varies in that regard.
There has only been two deposits of this found with Glenn finding the second deposit several hundred metres away from the first on the same ridge in 1994.
Unfortunately this is the only ridge in the world that produces this amazing material and is is now gone, swallowed up by a massive iron ore mine that just rips through everything to get to the iron ore.
I will post some pics on some pieces that I have on the go at the moment. You can see the hematite bands and if you look closely a couple of clear quartz bands and some nice jasper, which is typical of the better Marra Mumba.
Mike
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Thanks for your experiences and comments. Caution without the alarmism that if too often projected when risks are pointed out. Shop cleanup and machine cleanout are too often ignored because their health benefits are not appreciated. Thanks again for cogent explanation.
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Thank you so much for your thoughts on this as it had been a worry of mine. I appreciate the reminder about precautions.
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I have just finished shaping some beautiful old Marra Mumba rough...classic Marra Mumba material, with the original Marra Mumba palette of colours and patterns which makes it so rare and desirable.
I love my opal, but this stuff is right up there!
Enjoy,
Mike
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I cut these for an acquaintance some time back. I loved the subtle color changes in the material. I had bought some rough but it never turned out like these.
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Nice! No doubt some pieces cut better than others. The material varies a fair bit and some is pretty hard to get a nice polish, but it is rewarding when the planets align.
I like your shapes! 👍👍
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Just great. The colors and the shapes
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Great photos and, once again, invaluable info.
It's so good of you to post photos of the "real" thing. So many things in the lapidary world get mis-identified, and over time people become convinced that what they've always heard or read just has to be correct.
We appreciate the education.
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Here's one Robin just cut. Looks like it has similarities to your square shaped cab.
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Nice!
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Yeah nice...that is ‘Packsaddle’... You get nice landscapes in it and it is much easier to get a good polish than some of the other Marra Mumba material.
The Packsaddle material was mined in 1994, and is on the same ridge as the original Marra Mumba material mined in the early 80’s.
The black arches are magnesite bands.
Mike
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Thanks for the background info. We had looked at the Mindat database for the area, but historical info like that isn't easy to find.
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Hi Mike,
Your Marra Mumba seems to have been sold under different trade names here in the U.S. Mostly I see it sold as Marra Mamba and other varieties were sold as Tiger-Iron
Here are some I cut a while back.
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I know the difference between Marra mamba and tiger iron when I see it, but when I read the description, they sound much alike. The tiger iron has both tiger eye and hematite too. I’m not too sure about the jasper though? What is the technical difference that something is tiger iron and not Marta mamba? Personally, I feel the tiger iron always seems to have tight mostly parallel bands as opposed to forming pictures or having large areas of any one material, but I’m not sure that enters into consideration when making a differential determination?
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It is a little confusing. Tiger eye, was found in the 1970’s in the central highest hills in the Hamersley Ranges. Subsequent finds on Mount Brockman are within several hundred metres of the original deposits.
The brand Marra Mumba means that the tiger eye is from this region, and contains a mixture of tiger eye, beautiful coloured jasper and bands of magnetite. This doesn’t mean every stone cut will show all three, as some of the tiger eye bands can be really thick.
The other distinguishing Marra Mumba trait, is that the tiger eye forms in a mixture of colours, from yellow, gold, blue, and the classic bronze red.
Tiger iron comes from the Ord ranges some distance away. It generally has a higher iron content, but is distinctive in its banding which contains thinner golden bands of chatoyant tiger eye, with hematite and magnetite bands as well as jasper bands. The jasper bands can be deep red to lighter more subtle colouration as seen in the piece just above (the one correctly labelled tiger iron.
This sounds confusing I know...but you can quickly pick the two once you get used to seeing it. They are both fabulous stones, but the Marra Mumba is a lot trickier to cut in terms of achieving a good polish* which I am sure most of you have experienced..
The Packsaddle ( see my square stone) material whilst not containing the synonymous Marra Mumba tiger eye colours, nor the variety of jaspers often seen in Marra Mumba ( yellow, olive green, red ) is still technically ‘Marra Mamba’, as it was formed in the same iron formation very close to the original deposit. This material is harder and much easier to polish.
By the way, I sought this clarification direct from Glenn Archer (who found and mined both deposits).
I will go down to my workshop later and take a few pics of slabs of Marra Mumba and slabs of tiger iron... you guys will quickly see the difference.
Clear as mud!
Cheers,
Mike
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Sorry..forgot to mention..Ileney’s comments are spot on!
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Talk about authoritative info - straight from the fella' who found it is as good as it gets.
Glenn always has some Tiger Iron specimens at his booth in Quartzsite. Pieces that weight hundreds of pounds each!
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Here are some slabs...firstly Marra Mumba in this post. The tiger eye bands can be seen along with the jasper and magnetite bands. I like to cut stones that have a mixture of the three where possible as it highlights the contrasts and evidences that it is Marra Mumba.
The one larger slab of coppery red tiger eye with the Jasper is classic Marra Mumba, but the range of colours in the tiger eye bands has fantastic varieties of colours from blue to green and even the motley orange and red seen in the piece with the wide band.
Also see the distinctive golden Packsaddles material with the wonderful scenes... some pieces are incredibly chatoyant.
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Now some tiger iron slabs..
As Ileney hit on, the bands of Igor eye, jasper and hematite are more aligned, sometimes straight and in the better material curved ( makes for more interesting cabs).
This material is also spectacular and takes a great polish.
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This one is what I mean by including all elements. The upper RHS exhibits the coppery red tiger eye. Left of that and clearly defined is the section which is what Marra Mumba is all about to me...whereby all three (tiger eye, different colours of Jasper, and whisks of magnetite) are all mixed creating a spectacular speckled mixture of colours and even textures). Then the bottom of the stone are diametrically opposed bands of magnetite and even clear quartz ( if you look closely enough).
The mix is contrasting and especially pleasing to the eye, and in my opinion makes the stones more spectacular and definitely more interesting; and is what is distinctive about the Marra Mumba brand.
Hope the mud is becoming less clouded.
Mike
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Post that pic again ...looks all squashed up to me.
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Really beautiful material and cabs. :headbang:
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What a great stash of material you have! My problem with Marra Mamba has always been that it's such a work of art all by itself, I can't bring myself to cut it up. Into the too pretty to cut slab drawer it goes!
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Thank you for all that background information Mike, and all the fabulous pictures! I didn’t know the differences in where they were found and when. This is great to know.