ALBERT

Description: Results are presented on spectral, Moessbauer, static magnetic, petrographic, and compositional data for a Hawaiian palagonitic soil from Mauna Kea (HWMK1). It was found that reflectivity spectra of size separates smaller than 20 microns resemble spectra for Martian bright regions, while spectra of larger size separates show characteristics in common with spectra for Martian dark regions. Data on the HWMK1 soil are consistent with the partitioning of iron among the following minerals: olivine, titanomagnetite, hematite, and a superparamagnetic colored ferric oxide. These mineralogies are heterogeneously distributed within the soil with respect to both particle type and soil-particle diameter. The strongly magnetic titanomagnetite is associated with black particles and is responsible for the magnetic nature of the soil, while the colored weakly magnetic superparamagnetic ferric oxide and minor hematite are associated with orange particles.

Description: The effect of the matrix on the reflectivity spectra of nanophase (superparamagnetic) hematite (np-Hm) dispersed within the matrix was investigated in four series of powder samples containing np-Hm dispersed within discrete powder particles (of two size ranges) of silica gel and activated alumina. The spectral data show that matrix effects are large. Samples with the same Fe2O3 content can have np-Hm absorption edges characterized by very different positions and curvature and slope indices, while samples with equivalent absorption edges can have very different Fe2O3 concentrations. Thus, quantitative relationships between the positions of ferric absorption edges and Fe2O3 concentrations are unreliable without knowledge of matrix properties of the system. It is shown that it was possible to match the Fe2O3 concentration, magnetic properties, and spectral data for Martian surface material with a laboratory mixture whose only ferric-bearing phase was hematite.

Description: The 60013/14 double drive tube (62 cm deep) is one of three regolith cores taken 35-40 m apart in a triangular array on the Cayley plains at station 10' (LM/ALSEP), Apollo 16. This trio, which includes double drive tube 60009/10 (59 cm deep) and deep drill core 60001-7 (220 cm), is the only such array of cores returned from the Moon. The top 45 cm of 60013/14 is mature, as is surface reference soil 60601 taken nearby. Maturity generally decreases with depth, with soil below 45 cm being submature. The zone of lowest maturity (34 is less than or equal to I(sub s)/FeO is less than 50) extends from 46 to 58 cm depth, and corresponds to the distinct region of light-colored soil observed during core processing. In the other two cores, most of the compositional variation results from mixing between fine-grained, mature soil with 10-11 micro-g/g Sc and coarse-grained ferroan anorthosite consisting of greater than 99% plagioclase with less than 0.5 micro-g/g Sc. This is most evident in 60009/10 which contains a high abundance of plagioclase at about 54 cm depth (minimum Sc: 3-4 micro-g/g); a similar zone occurs in 60001-7 at 17-22 cm (MPU-C), although it is not as rich in plagioclase (minimum Sc: 6-7 micro-g/g). Compositional variations are less in 60013/14 than in the other two cores (range: 7.9-10.0 micro-g/g Sc), but are generally consistent with the 'plagioclase dilution' effect seen in 60009/10, i.e., most 60013/14 samples plot along the mixing line of 60009/10. However, a plagioclase component is not the cause of the lower maturity and lighter color of the unit at 46-58 cm depth in 60013/14. Many of the samples in this zone have distinctly lower Sm/Sc ratios than typical LM-area soils and plot off the mixing trend defined by 60009/10. This requires a component with moderately high Sc, but low-Sm/Sc, such as feldspathic fragmental breccia (FFB) or granulitic breccia. A component of Descartes regolith, such as occurs at North Ray Crater (NRC) and which is rich in FFB, could account for the composition of these soils (i.e., a 3:1 mixture of 60601 and NRC soil). It seems unlikely that NRC ejecta would occur half a meter deep at the LM station, thus this low-Sm/Sc component may result from an older, local crater that penetrated the Cayley surface layer and excavated underlying Descartes material, as did North Ray Crater. There is no evidence for such a unit or component in the other two cores. Soil below the light-colored unit (58-62) cm has 'typical' Sm/Sc ratios, but the lowest absolute Sc concentrations, i.e., it is compositionally equivalent to a mixture of surface soil and plagioclase such as that in ferroan anorthosite. This is the only soil that might be related to the plagioclase-rich units in the other two cores. Except for the mature soil at the top of each core and, perhaps, the plagioclase-rich layers, there is little compositional evidence for any common unit among the three cores. Soil corresponding to the mare-glass-bearing unit (MPU-B) and regolith-breccia-bearing unit (MPU-A) of 60001-7 do not occur in 60013/14 or 60009/10.

Description: Visible and near-IR spectral data for some palagonitic soils from Mauna Kea, Hawaii, are similar to corresponding spectral data for Mars. It is important to understand the composition, distribution, and mineralogy of the ferric-bearing phases for the best spectral analogues because the correspondence in spectral properties implies that the nature of their ferric-bearing phases may be similar to those on Mars. In order to constrain interpretations of the Martian data, a variety of palagonitic soils should be studied in order to establish to what extent differences in their spectral data correspond to differences in the mineralogy of their ferric-bearing phases. Spectral (350-2100 nm), Mossbauer, magnetic, and some compositional data for one of a suite of Hawaiian palagonitic soils are presented. The soil (HWMK1) was collected below the biologically active zone from the sides of a gully cut at 9000 ft elevation on Mauna Kea. The soil was wet sieved with freon into seven size fractions less than 1 mm.

Description: Samples containing variable amounts of superparamagnetic hematite (sp-Hm) were prepared by a method in which the sp-Hm particles were dispersed throughout larger particles of silica gel, and the optical and magnetic properties of these samples were compared with those of larger-diameter hematite (bulk-Hm). It is shown that the optical properties of sp-Hm are different from those of bulk-Hm. Implications of the results for mineralogical interpretations of spectral data for the Martian surface and its terrestrial analogues are discussed. It is concluded that features resulting from ferric iron in the Martian spectral data and the results of the Viking magnetic properties experiment are both consistent with hematite present as both sp-Hm and bulk-Hm; the hematite particles most likely occur in pigmentary form, i.e., as particles dispersed throughout the volume of a spectrally neutral material.

Description: The effect of substituting iron by aluminum in polymorphs of Fe2O3 and FeOOH on their reflectivity characteristics was investigated by comparing data on visible and NIR reflectivities and on static magnetic, XRD, and Moessbauer properties for a family of aluminum-substituted hematites alpha-(Fe,Al)2O3, with compositions where the values of the Al/(Al+Fe) ratio were up to 0.61. Samples were prepared by oxidation of magnetite, dehydroxylation of goethite, and direct precipitation. The analytical methods used for obtaining diffuse reflectivity spectra (350-2200 nm), Moessbauer spectra, and static magnetic data are those described by Morris et al. (1989).