Hisingerite

Abstract: X-ray diffraction patterns of the three samples analyzed by Curiosity's Chemistry and Mineralogy (CheMin) instrument during the first year of the Mars Science Laboratory mission—the Rocknest sand, and the John Klein and Cumberland drill fines, both extracted from the Sheepbed mudstone—show evidence for a significant amorphous component of unclear origin. We developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from CheMin data. In turn, the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions (all oxides ≥ 0 wt %): 21–22 wt % for Rocknest and 15–20 wt % for Cumberland, in good agreement with estimates derived from the diffraction patterns (~27 and ~31 wt %, respectively). Despite obvious differences between the Rocknest sand and the Sheepbed mudstone, the amorphous components of the two sites are chemically very similar, having comparable concentrations of SiO2, TiO2, Al2O3, Cr2O3, FeOT, CaO, Na2O, K2O, and P2O5. MgO tends to be lower in Rocknest, although it may also be comparable between the two samples depending on the exact composition of the smectite in Sheepbed. The only unambiguous difference is the SO3 content, which is always higher in Rocknest. The observed similarity suggests that the two amorphous components share a common origin or formation process. The individual phases possibly present within the amorphous components include: volcanic (or impact) glass, hisingerite (or silica + ferrihydrite), amorphous sulfates (or adsorbed SO42−), and nanophase ferric oxides.

Abstract: Clayey fragments colored deep bluish-green are widely found in glassy rhyolitic tufts at Oya, Tochigi Prefecture. In room-air the color changes to black or gray within one hour and finally to brown in a few weeks. The fragments are composed of an intimate mixture of two kinds of smectite: a ferrous iron-rich smectite (IR) with bo : 9.300 ~; and an iron-poor smectite(lP) with bo = 9.030 A. Microscopic examination shows a vesicular texture and that IR occurs at the core and IP at the mar- ginal parts of each vesicle. Analysis by EPMA gave the following structural formulas: IR, (Na0,60- Ko.04Ca0.44) (Mg~.04Fe 2+ A1o02) (Sir.36All.64)O20(OH)4; IP, (Na0.~2K0.08Ca0.26) (Mgog0Fe2+.A1254) 3"98 " ' O'9a ' (SiT.66A1o.~4)O20(OH)4. IR has a much larger amount of iron in trioctahedral sites than that found in any earlier data. Acid-dissolution data, infrared absorption spectra, Eh-values, and DTA and TG curves are also given. Ferrous iron in the structure is easily oxidized in room air with loss of protons from the clay hydroxyls and with contraction of the lattice. We call the IR before and after oxidation the ferrous and ferric forms, respectively, of iron-rich saponite. They strongly suggest the existence of the iron- analogue of saponite. On exposed weathered surfaces in the field, brown fragments tend to be differ- entiated into two parts: one light yellow montmorillonite-beidellite; the other a brown incrustation due to hisingerite.

Abstract: Hisingerite, first described in 1810, has been variously regarded as noncrystalline, as a septechlorite, as ferric allophane, as ferric halloysite and as poorly crystalline nontronite. Hisingerite from the original localities of Gillinge and Riddarhyttan in Sweden has a composition close to Fe 2 O 3 .2SiO 2 .2H 2 O. X-ray diffraction (XRD) analysis of Riddarhyttan hisingerite yields very broad maxima at 7.7, 4.44, 3.57, 2.56, 2.26, 1.69 and 1.54 Aa, and that from Gillinge is similar. Cation exchange capacities are 2.2 meq/100 g (Riddarhyttan) and zero (Gillinge). Transmission electron microscopy (TEM) shows a fabric of concentric spheres and part spheres, with diameters of about 140 Aa and walls up to six 7-Aa layers thick. High-resolution images of the sphere walls reveal a 2-layer structure similar to that of kaolinite. A calculated diffraction pattern based on a model of 4 concentric shells of ferric kaolinite structure matches the observed pattern quite closely. Some other hisingerites, notably that from Bellevue King Mine, Idaho, show 10-Aa layers as well as 7-Aa layers, and this hisingerite has a CEC of 32 meq/100 g and a weak 15.5-Aa X-ray reflection in addition to a pattern similar to Riddarhyttan hisingerite. It is concluded that hisingerite is a curved ferric 7-Aa 1:1 layer silicate analogous to halloysite, and that many of the hisingerites reported in the literature contain admixed nontronite.