Samples are from a site where excavators claimed the sediments cut up their hands, leading them to think that a high amount of volcanic ash is present in sediment samples. I am thinking of using water and beakers to sort heavy and light fractions. Anyone have better ideas?
Obviously I don't know the specific circumstances here, but it may be possible to apply a densitiy separation method. Assuming that you are dealing with microscopic glass shards, I would recommend sieving followed by separation using something like sodium polytungstate. Methods for this are available in the scientific literature (e.g. Blockley et al., 2005). Tephra will can be separated from most minerals using this method, the density difference (especially for rhyolites) is sufficient to get good extractions. I hope this helps. I agree with the above reply though, it would be wise to check a raw sample first before doing all this.
Obviously I don't know the specific circumstances here, but it may be possible to apply a densitiy separation method. Assuming that you are dealing with microscopic glass shards, I would recommend sieving followed by separation using something like sodium polytungstate. Methods for this are available in the scientific literature (e.g. Blockley et al., 2005). Tephra will can be separated from most minerals using this method, the density difference (especially for rhyolites) is sufficient to get good extractions. I hope this helps. I agree with the above reply though, it would be wise to check a raw sample first before doing all this.
I agree with the approaches outlined above. separation of ash from background sediment is often challenging. Normally the first stage would be careful and meticulous sampling in the field - but this doesn't seem an option in your case given the sample is extracted in a quarry(?). A possible analytical strategy may be as follows:
1) Use binocular microscope to observe (dried) material to determine the nature of ash particles versus sediment particles. Is there a shape, compositional or a size difference?
2) If the answer to any of these is affirmative then choose sieving (size fraction difference) or heavy liquid separation (compositional difference), as appropriate. Density separation will only succeed if there is sufficient density contrast between ash and sediment particles (e.g., compositional or vesiculated/pumice etc.). Use/adopt methodologies outlined in key papers - those by Simon Blockley (RHUL0 or by John Stevenson (Edinburgh), or Victoria Smith (Oxford).
3) Glass shards will provide the (degassed) bulk geochemistry of the magma. you will need several grammes of material for XRF. A better method in your case may be ICP since this requires small aliquots and gives a large suite of elements. If material is really sparse, you could use a microprobe (both RHUL and Oxford have a track record in cryptotephra studies - very small particles).
4) It should be possible to fingerprint the chemistry of the ash to a particular eruptive source. Start with historically active volcanoes in the vicitinty, then widen search both geographically and temporally. There is substantial literature on this subject - especially wrt Icelandic volcanoes.
Good Luck!
Hi all, and thank you very much for your constructive comments! I now have a good idea on how to proceed with these samples.
Dry sample or in suspension? If dry, then a riffler/shaker table? That's used for sorting irregular diamond from more symmetrical (octahedrons) shapes. You should be able to find a local supplier in your neck of the woods. I agree totally with a microscopic examination - tells you so much.
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