The optical spectroscopic comparison of the ferric iron tetrameric clusters in amarantite and
leucophosphite

George R. Rossman
 Division of Geological and Planetary Sciences
California Institute of Technology
Pasadena, CA  91125

Abstract

Optical absorptionspectraand magneticsusceptibilitydataarepresentedfor two minerals, amarantite,Fe2(SO4)2O·7H2O, and leucophosphite, K2[Fe4(OH)2(H2O)2(PO4)4]·2H2O,which contain nearly planar ferric iron tetrameric units. These data are compared to corresponding single crystal optical data for phosphosiderite, FePO4·2H2O. Pronounced enhancement of the intensities of the absorption bands and absorption anisotropy, which are associated with the strong antiferromagnetic coupling (muFe.= 2.53 B.M. at 297°K) of the oxobridged amarantite tetramer, is noted for amarantite. Synthetic leucophosphite exhibits a much weaker antiferromagnetic interaction (muFe = 5.13 B.M.). Natural leucophosphite displays littleoptical absorption anisotropy and much lower absorption intensity than amarantite.
spectra
  The optical spectrs of amarantite and leucophospite in 0.10 mm thick sections.
last updated: 23-Jul-2023