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Published June 1993 | public
Journal Article

Metamict and chemically altered vesuvianite

Abstract

Partly metamict vesuvianite samples from two localities were examined and compared. The unit cell of one is enlarged owing to volume expansion caused by the buildup of radiation damage. The other sample sustained enough damage to exclude accurate determination of unit-cell parameters. BSE imaging shows that both samples have undergone chemical alteration, and electron-microprobe data indicate that the alteration has resulted in a heterogeneous distribution of radionuclides on the micrometer scale. HRTEM and SAED analyses reveal a wide variation in the extent of alpha-recoil damage, which corresponds to the heterogeneous distribution of the radionuclides. The progressive stages of metamictization also are observed in detail with TEM. Partly metamict vesuvianite recrystallizes over the range 600-850°C, which is broader than the range found in other metamict silicates. Combined thermogravimetric analysis and isothermal annealing show that, upon heating (in N_2 or Ar), metamict vesuvianite begins to recrystallize at 600°C, and at 900°C decomposes in to the multiphase assemblage grossular+ gehlenite+wollastonite. Unpolarized IR spectra of both vesuvianite samples are similar and also resemble those of radiation-damaged zircon and titanite, suggesting that the major structural features of the aperiodic state are similar for complex ceramics of different composition.

Additional Information

© 1993 Mineralogical Association of Canada. Received March 23, 1992, revised manuscript accepted September 2, 1992. Sample V73 was collected by a prospector, the late Bob Beal, who then brought the sample to Jack A. Adams, formerly of the U.S. Geological Survey, for identification. By XRD of the as-found and heated sample Adams identified the sample as metamict vesuvianite and later donated it to the Department of Geology, UNM. Roger Aines provided us with assistance in preliminary IR measurements of sample V53. Useful comments and suggestions were provided by Joe Blatz and Fred Shmuck, who reviewed the manuscript. NSERC of Canada provided assistance in the form of fellowships to RKE, operating grants to FCH and LAG, and an infrastructure grant to FCH. This work was also supported by Basic Energy Sciences of DOE, grant #DE-FGO4-84ER45099 to RCE. TEM was done in the Electron Microbeam Analysis Facility of the Department of Geology, UNM, supported in part by NSF, NASA, BES and the state of New Mexico. Research done at ORNL was supported by the Division of Materials Sciences. DOE contract #DE-AC05-84OR21400 with Martin Marietta Energy Systems, and at Caltech by NSF grant #EAR-8916064.

Additional details

Created:
August 22, 2023
Modified:
October 23, 2023