Search

Compositional data and Fe&sup3+;/ΣFe ratios obtained by electron microprobe and Mössbauer analyses are given for a suite of three amphibole and amphibole-asbestos samples collected from the former vermiculite mine near Libby, Montana. A crystal structure analysis, compositional data, and Fe&sup3+;/ΣFe values for two samples from a previous study are also reported. The results confirm the conclusion drawn in the previous study that these amphiboles are dominantly compositions ranging from winchite to richterite. Mössbauer spectroscopy yielded Fe&sup3+;/ΣFe ratios from 58% to 72% for the five samples. The crystal structure was determined for a single crystal selected from a bulk sample. Its formula (as determined by electron microprobe analysis and Mössbauer spectroscopy) is (K[sub0.19] Na[sub0.32])[subA](Na[sub0.85] Ca[sub1.12]Mn[sub0.03])[subB](Mn[sub0.01]Mg[sub4.43]Feb[sup.3+, sub0.34]Fe[sup2+, sub0.19]Ti[sub0.01]Al[sub0.02]) Al[sub0.03]Si[sub7.97]O[sub22])(OH[sub1.63]F[sub0.37]). The refinement was carried out based on space group C2/m, with a = 9.879(2), b = 18.024(3), c = 5.288(1 ) Å β = 104.377(3)° and using data collected at room temperature. Mg is partitioned among the M1, M2, and M3 sites. All of the Fe&sup3+; occupies M2, while Fe&sup2+; is split between M2 and M3; Ca and Na fill the M4 site, while Na and K occupy the partially filled A site. The A-site occupancy is calculated as 0.51 based on chemical data, but only 0.48 based on X-ray diffraction results. Minerals with the former values would be classified as richterite and those with the latter as winchite. [ABSTRACT FROM AUTHOR]