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Proposed nomenclature for samarskite-group minerals: new data on ishikawaite and calciosamarskite

Published online by Cambridge University Press:  05 July 2018

S. L. Hanson ,
W. B. Simmons ,
A. U. Falster ,
E. E. Foord  and
F. E. Lichte
S. L. Hanson
Affiliation:
University of Utah, Department of Geology and Geophysics, 717 WBB, Salt Lake City, Utah, 84112-1183
W. B. Simmons
Affiliation:
University of New Orleans, Department of Geology and Geophysics, New Orleans, Louisiana 70148
A. U. Falster
Affiliation:
University of New Orleans, Department of Geology and Geophysics, New Orleans, Louisiana 70148
E. E. Foord
Affiliation:
MS 905, U. S. Geological Survey, Box 25046, Denver Federal Center, Denver, Colorado 80225
F. E. Lichte
Affiliation:
MS 905, U. S. Geological Survey, Box 25046, Denver Federal Center, Denver, Colorado 80225
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Abstract

The current definition of samarskite-group minerals suggests that ishikawaite is a uranium rich variety of samarskite whereas calciosamarskite is a calcium rich variety of samarskite. Because these minerals are chemically complex, usually completely metamict, and pervasively altered, their crystal chemistry and structure are poorly understood. Warner and Ewing (1993) proposed that samarskite is an A3+B5+O4 mineral with an atomic arrangement related to α-PbO2. X-ray diffraction analyses of the recrystallized type specimen of ishikawaite and the Ca-rich samarskite reveal that they have the same structure as samarskite-(Y) recrystallized at high temperatures. Electron microprobe analyses show that the only significant difference between samarskite-(Y), ishikawaite, and calciosamarskite lies in the occupancy of the A-site. The A-site of samarskite-(Y) is dominated by Y+REE whereas the A-site of ishikawaite is dominantly U+Th and calciosamarskite is dominantly Ca. Additionally, a comparison of these data to those of Warner and Ewing (1993) show that in several cases Fe2+ or Fe3+ are dominant in the A-site. We propose that the name samarskite-(REE+Y) should be used when one of these elements is dominant and that the mineral be named with the most abundant of these elements as a suffix. The name ishikawaite should be used only when U+Th are dominant and the name calciosamarskite should only be used when Ca is the dominant cation at the A-site. Finally, because of the inability to quantify the valence state of iron in these minerals, the exact nature of the valence state of iron in these minerals could not be determined in this study.

Keywords

samarskite groupishikawaitecalciosamarskitemetamict state
Type
Research Article
Information
Mineralogical Magazine , Volume 63 , Issue 1 , February 1999 , pp. 27 - 36
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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Footnotes

1

Present address: Earth Sciences Department, Adrian College, Adrian, MI 49221, U.S.A..

*

Deceased 8 January 1998

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