W.B. Simmons A.U. Falster E.E. Foord F.E. Lichte S.L. Hanson 1999 <p><span>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&nbsp;</span><i><span class="italic">A</span></i><span class="sup">³⁺</span><i><span class="italic">B</span></i>^{<span class="sup">5+</span>}<span>O</span>_{<span class="sub">4</span>}<span>&nbsp;mineral with an atomic arrangement related to α-PbO</span>_{<span class="sub">2</span>}<span>. 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&nbsp;</span><span class="italic">A</span><span>-site. The&nbsp;</span><span class="italic">A</span><span>-site of samarskite-(Y) is dominated by Y+</span><span class="italic">REE</span><span>&nbsp;whereas the&nbsp;</span><span class="italic">A</span><span>-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 Fe</span>^{<span class="sup">2+</span>}<span>&nbsp;or Fe</span>^{<span class="sup">3+</span>}<span>&nbsp;are dominant in the&nbsp;</span><span class="italic">A</span><span>-site. We propose that the name samarskite-(</span><span class="italic">REE</span><span>+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&nbsp;</span><span class="italic">A</span><span>-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.</span></p> application/pdf 10.1180/002646199548286 en Cambridge University Press Proposed nomenclature for samarskite-group minerals: new data on ishikawaite and calciosamarskite article