Try high gradient magnetic separation (HGMS). Amazingly, most minerals are magnetic in some way (diamagnetic, paramagnetic) and even quartz (diamagnetic) and feldspar (paramagnetic) of the right grain size can be separated in a simple HGMS set up.
the method is described here:
High-gradient magnetic separation applied to sand-size particles: An example of feldspar separation from mafic minerals
Author(s): HILLIER, S; HODSON, ME
Source: JOURNAL OF SEDIMENTARY RESEARCH Volume: 67 Issue: 5 Pages: 975-977 Published: SEP 1997
Dear Mr. Pandey:
Separation of quartz and feldspar s.s.s using magnetic separation techniques are rather doubtful in practice. Neither their magnetic susceptibility values nor their specific gravity are so distinct from each other that theyas as a useful tool for mineral separation. Both minerals can be intergrown with Fe giving rise to special modifications such as carnelian which may have an effect on the magnetic properties.
There exists a characteristic difference between the two minerals. It is the cleavage. Feldspar shows a perfect cleavage which favors its grinding and disintegration, a fact which is stimulated when undergoing supergene or hypogene alteration leaving behind an almost powdery aggregate of kaolinized feldspar. Exerting mild pressure provokes the feldspar to disintegrate into smaller particles or a powdery substrate while quartz which is less vulnerable to these alteration and shows no cleavage will maintain its grain size; sieving and washing helps you get rid of the feldspar in the aftermaths. It means simply copying what is done in the most efficient processing plant called nature.
Best regards
Harald G. Dill
Dear Mr. Pandey,
sometimes differ both minerals by color (feldpar whitish, quartz grayish), then could serve optical sorting (basic info p.e. on https://en.wikipedia.org/wiki/Optical_sorting).
Regards
Jaromir Tvrdy
Thank you sir for yours scholarly notions. Objective of the separation of quartz and feldspar minerals is that we are using coarse grains quartz for optical stimulated luminescence (OSL), so it necessitates being very precise. Actually, we had used density separation principle; and used intermediate specific density chemicals such as sodium polytungstate and boromoform. Meanwhile, we worried about that using these chemicals may bleach the sediments.
Hello!
regarding the purification of fine grain quartz, for optically stimulated luminescence dating (OSL), the most successful approach so far consist in using hexafluorosilicic acid, or, alternatively, very weak hydrofluoric acid.
Jackson, M.L., Sayin, M., Clayton, R.N., 1976. Hexafluorosilicic acid reagent modification for quartz isolation. Soil Science Society of America Journal 40, 958-960.
Heavy liquid separation will not 'bleach' the luminescence signal, as long as you operate in a dark lab.
I'm not a chemist. I have experience with both type of acid, as does the optically stimulated luminescence dating community. All I can say is that both are very efficient at dissolving feldspar (and many other silicates). With Hydrofluoric acid (HF), given time, it will also dissolve quartz.
For hexafluorosilicic acid, it as no discernible effect on quartz. Hence, it can be of use with 'fine grain' (I presume fine silt is what Pandey implies here). There is a caveat, though. At room temperature, the hexafluorosilicic will produce HF by dissociation, in small concentration.The hexafluorosilicic must be purified (of HF) before introducing it to your sample. It must be carried out at cold temperature, to prevent renewed formation of HF by dissociation.
It could also be separated by density of both minerals, with liquids.
Quartz grains are almost rounded while feldspar is angular. Upon this criterion you can use specific screens.
Thank you everyone for your scholarly insights. I have treated the fine sediment with HF concentrate for 2 hours, and it dissolved the feldspar. We have also cross-check it with IRSL test. Quartz mineral does not produce luminescence at room temperature; and the result was very accurate.
You can use flotation (anionic-cationic coditions or with amine colloctor and HF) or by using an aqueous solution of sodium polytungstate.
Sodium polytungstate can be used, it can be dissolved in water to get a solution of density ~2.58 gm/cc. The density of feldspar is ~2.56 and that of quartz is ~2.62. So quartz will settle down and feldspar will float.
I guess you already have got your answers from the earlier inputs. My 2-bits of experience:
1. the best way of separating quartz and feldspars (assuming it is dominantly alkali feldspars) is manual separation under a reflecting microscope with sufficient magnification. Their densities and RI are close to each other, but the differences in cleavage and crystalline form are rather obvious.
2. any chemical treatment (with or without dilute acids) is capable of removing surface coatings [which is good], but also affecting the luminosity of the mineral grains [which is not so good]. Avoidable if possible.
mechanical and magnetic resonance separators will provide up to 75% enrichment, but not give a clear separation.
Hope that helps.
It already has many valid answers, but you can use liquids with different densities, so that the quartz of precipitate and the feldspar floats in the liquid. Until you find the optimum.
Thank you everyone for your kind suggestion and insightful answers. Meanwhile, I am using Frantz Isodynamic Magnetic separator with different setting and it has given very good result.
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