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Sandeep, I have done lots of SEM work on Triassic tuffs from the Southern Alps (Austria & Italy). The rhyolitic tuffs contain many zircons. Some of them show spongy texture and various etching features. The backscattered image of the SEM could also see Zr- and Y-rich clouds around altered zircons. The tuffs are altered by burial diagenesis und may be a postdepositional hydrothermal event. See also: Obenholzner, J. H. & Heiken, G.: Textural studies of altered/metamorphosed tuiffs and secondary REE,-, Zr- and Y-minerals. Annalen des Naturhistorischen Museums in Wien, 100A, 13-38, Vienna 1999. There is also an abstract at AGU Spring meeting 2000. best wishes Johannes H. Obenholzner NHM-Mineralogie Postfach 417 A-1014 Vienna Austria Dr Sandeep Singh wrote: > Dear All > > Happy New year. > > I am working on SHRIMPING (ion probe mass-spectrometry) the Himalayan > zircon having metamorphic overgrowth. During this I have come across some > of the zircons which have spongy texture. Can anybody give me some > references on that which explains the phenomenon. > > Sandeep > > *********************************************************************** > Dr. Sandeep Singh > (office) (residence) > > BOYSCAST Fellow 5/54, Melville Pde, > Centre for Global Meltallogeny South Perth, WA, 6151 > Department of Geology and Geophysics Australia > University of Western Australia > Nedlands, Western Australia 6907 phone: +61 (08) 9368 4035 (res.) > AUSTRALIA > > phone: +61 (08) 9380 2640 (off.) > Fax: +61 (08) 9380 1178 > e-mail: [log in to unmask] > website: www.sandeepsingh.20m.com > ********************************************************************