HISINGERITE - A FERRIC KAOLIN MINERAL WITH CURVED MORPHOLOGY

Hisingerite, first described in 1810, has been variously regarded as n oncrystalline, as a septechlorite, as ferric allophane, as ferric hall oysite and as poorly crystalline nontronite. Hisingerite from the orig inal localities of Gillinge and Riddarhyttan in Sweden has a compositi on close to Fe2O3. 2SiO(2). 2H(2)O. X-ray diffraction (XRD) analysis o f Riddarhyttan hisingerite yields very broad maxima at 7.7, 4.44, 3.57 , 2.56, 2.26, 1.69 and 1.54 Angstrom, and that from Gillinge is simila r. Cation exchange capacities are 2.2 meq/100 g (Riddarhyttan) and zer o (Gillinge). Transmission electron microscopy (TEM) shows a fabric of concentric spheres and part spheres, with diameters of about 140 Angs trom and walls up to six 7-Angstrom layers thick. High-resolution imag es of the sphere walls reveal a 2-layer structure similar to that of k aolinite. A calculated diffraction pattern based on a model of 4 conce ntric shells of ferric kaolinite structure matches the observed patter n quite closely. Some other hisingerites, notably that from Bellevue K ing Mine, Idaho, show 10-Angstrom layers as well as 7-Angstrom layers, and this hisingerite has a CEC of 32 meq/100 g and a weak 15.5-Angstr om X-ray reflection in addition to a pattern similar to Riddarhyttan h isingerite. It is concluded that hisingerite is a curved ferric 7-Angs trom 1:1 layer silicate analogous to halloysite, and that many of the hisingerites reported in the literature contain admired nontronite.