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Ochreous precipitates containing 5.5-69.8 g/kg As were isolated from mine drainage in Finland and were composed of schwertmannite, ferrihydrite, and goethite. Schwertmannite formation was favored at pH 3-4, but its structure was degraded at high As levels. A series of coprecipitates were therefore prepared from mixed iron arsenate/sulfate solutions to define the limits of schwertmannite stability. Schwertmannite was replaced as the dominant phase by a poorly crystalline ironIII hydroxy arsenate (FeOHAs) when As/Fe mole ratios exceeded 0.15. The FeOHAs gave an X-ray diffraction pattern similar to that obtained from an "amorphous" ironIII arsenate (As/Fe = 1.0) with broad peaks at 0.30 and 0.16 nm. The FeOHAs possessed a magnetic hyperfinefield of 41.9T at 4.2 K that was intermediate to those of schwertmannite (46.1 T) and the ironIII arsenate (24.8 T). These data indicate a strong disruptive effect of arsenate on magnetic ordering and structure development in schwertmannite. Equilibration of 0.01 M arsenate solutions with freshly prepared schwertmannite and 2-line ferrihydrite at pH 3.0 for up to 60 d gave sorbed As contents of 175 and 210 g/kg, respectively. Arsenate sorption degraded the host schwertmannite and ferrihydrite, perhaps due to the formation of an FeOHAs surface phase.

Schwertmannlte is a new oxyhydroxysulphate of iron from the Pyh~isalmi sulphide mine, Province of Oulu, Finland. It occurs there, and elsewhere, as an ochreous precipitate from acid, sulphate-rich waters. Associated minerals at other localities may include jarosite, natrojarosite, goethite and ferrihydrite. Schwertmannite is a poorly crystalline, yellowish brown mineral with a fibrous morphology under the electron microscope. A high specific surface area in the range of 100 to 200 m2/g, rapid dissolution in cold, 5 M HCI or in ammonium oxalate at pH 3, and pronounced X-ray diffraction line broadening are consistent with its poorly crystalline character.Colour parameters for the type specimen as related to CIE illuminant C are L ~ = 53.85, a* = + 15.93, and b ~ = +47.96. Chemical analysis gives FezO3, 62.6; SO3, 12.7; CO2, 1.5; HzO-, 10.2; H20 +, 12.9; total 99.9 wt.%. These data yield an empirical unit cell formula of FelsOIs(OH)9.6(SO4)3.2.10H20 after exclusion of CO2 and HzO-. The most general simplified formula is Fe16O16(OH)y(SO4)z.nH20, where 16 -y = 2z and 2.0 ~< z ~< 3.5. Schwertmannite has a structure akin to that of akaganrite (nominally 13-FeOOH) with. a doubled c dimension. Its X-ray powder diffraction pattern consists of eight broad peaks [dobs in A(Iobs) (hk/)] 4.86(37)(200,111); 3.39(46)(310); 2.55 (100)(212); 2.28(23)(302); 1.95(12)(412); 1.66(21)(522); 1.51(24)(004) M6ssbauer data show the Fe in schwertmannite to be exclusively trivalent and in octahedral coordination; it has a Nrel temperature of 75 __+ 5 K and a saturation magnetic hyperfine field of about 45.6 T. Pronounced asymmetry of the M6ssbauer spectra indicates different locations for Fe atoms relative to SO4 groups in the structure. The name is for Udo Schwertmann, professor of soil science at the Technical University of Munich.

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We investigated the effect of fire intensity from slash‐and‐burn agriculture on the mineralogy of Oxisols in the Sepunggur area, Jambi Province, Sumatra, Indonesia, in both field and laboratory experiments. Samples were collected from two depths (0–5 and 5–15 cm) at locations exposed to 100, 300, 600, and >600°C surface temperatures during the burns. Soils under forest and slashed vegetation were collected as controls. The pre‐burn soil mineralogy was dominated by kaolinite, gibbsite, anatase, and goethite. Changes in soil properties with burning were most pronounced in the 0‐ to 5‐cm layer. Burning the topsoil led to coarser textures, especially at temperatures exceeding 600°C. Heat reduced the gibbsite and kaolinite concentrations and converted goethite into ultra‐fine maghemite, thus increasing the magnetic susceptibility of the samples. The conversion of goethite did not take place until water in the samples had vaporized. Addition of organic matter to soil with a low organic C content before heating increased the magnetic susceptibility, indicating that organic matter was necessary (and limiting) for the complete conversion of goethite. Coarse‐grained magnetite particles were present prior to and after the burning and, therefore, were not pyrogenic. Magnetic susceptibility measurements were highly discriminatory among heat treatments, whereas x‐ray diffraction (XRD) was much less sensitive to fire‐induced changes in mineralogy. Our research showed that severe burning had drastic effects on soil mineralogy, but changes should also be expected at lower fire intensities. Further research is needed to determine how important these changes in soil mineralogy are for nutrient availability in the growing season after the burn.

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Abstract--Reference smectites were examined to determine relationships between Li uptake, cationexchange capacity (CEC), and octahedral layer charge after Li saturation and heating at 250~ (HofmannKlemen effect). Direct measurements of exchangeable Li after heating led to overestimates of charge reduction due to entrapment of Li in collapsed interlayers. Expansion ofinterlayers by sequential washings with 1 N MgCI2, 0.01 N MgCI:, and ethanol and subsequent determinations of exchangeable Mg provided accurate measurements of reduced charge. The CEC reductions observed in dioctahedral samples as a result of Li saturation and heating equaled octahedral charge values derived from published mineral formulae, and interlayer charge estimates obtained by alkylammonium exchange confirmed that measured CEC reductions were a consequence of uniform decreases in octahedral layer charge.Dioctahedral specimens retained 1 to 10 meq/100 g of non-exchangeable Li in excess of CEC reduction and were acidified in direct proportion to their total Fe contents, apparently as a result of the deprotonation of structural hydroxyl groups. Mild acid treatment reprotonated these hydroxyl groups, released excess Li, and resulted in total Li contents comparable to measured CEC reductions. Heating (250~ Mgsaturated hectorite induced a loss of octahedral Li, acidification, and a reduction of CEC, indicating that Mg had partially replaced octahedral Li. These results suggest that octahedral Li is mobile at low temperatures and that cation movement into or out of the octahedral sheet is favored if the layer charge is reduced.