Basalt Grains Research Articles

Experimental Studies of Packing Material Stability

ABSTRACTThe Basalt Waste Isolation Project is conducting experiments to assess the stability of bentonite (sodium montmorillonite)and crushed basalt as waste package packing materials in a nuclear waste repository in basalt. The experiments are designed to identify changes in physical, chemical, and mineralogical properties that these materials could undergo in the repository environment. A series of bentonite dehy-dration experiments showed that after 1 year at 370°C the clay's structural and swelling properties were preserved and only reversible dehydration occurred. At 440°C, however, irreversible dehydration, collapse of the clay structure, and loss of swelling ability took place. Hydrothermal tests using bentonite, or an equal mixture of bentonite and basalt, along with synthetic groundwater, were also conducted. Abentonite + water experiment showed negligible structural alteration at 200°C, although some iron enrichment of the clay occurred. At 300°C, partial conversion of the mont-morillonite to an iron- and potassium-rich smectite occurred, along with the formation of secondary quartz and albite. An experiment in the basalt + bentonite + water system at 150°C resulted in partial etching of the basalt grains, but no detectable change in rock or clay mineralogy. At 300°C, the basalt was strongly etched. Furthermore, iron- and potassium-rich smectite apparently replaced montmorillonite as the dominant clay, and secondary silica, zeolites, and minor feldspar were formed. These mineral assemblages are thought to be metastable at 300°C, based on natural analogs. The kinetics and reaction paths of further transformations of packing materials are important areas for continued study.

Nature of magnetic grains in basalts and implications for palaeomagnetism : Radhakrishnamurty, C., S. D. Likhite, E. R. Deutsch and G. S. Murthy, 1978. Proc. Indian Acad. Sci., 87(A)(Earth & Planetary Sci. 4(11): 235–243

Nature of magnetic grains in basalts and implications for palaeomagnetism : Radhakrishnamurty, C., S. D. Likhite, E. R. Deutsch and G. S. Murthy, 1978. Proc. Indian Acad. Sci., 87(A)(Earth & Planetary Sci. 4(11): 235–243

Nature of magnetic grains in basalts and implications for palaeomagnetism

Investigations involving temperature dependence of low-field susceptibility and of low- and high-field hysteresis have been carried out on more than one thousand basalt samples of ages ranging from less than 3 million years to more than 1 billion years. Combined application of these measurements makes it possible to distinguish rapidly the effective particle sizes and oxidation states of the magnetic minerals in the rock.One interesting finding is that, in basalts of widely different ages, a strongly cation-deficient phase of magnetite having distinct magnetic properties predominates over other types of magnetic grains inferred to be present. Properties attributable to multidomain magnetite were found often in basalts older than Cretaceous, but seem to be present only occasionally among the younger basalts. Despite the fact of a frequent association of magnetite with titanium in basalts, results of our tests carried out on such basalts do not in general show a magnetic behaviour consistent with the magnetic material being a solid-solution titanomagnetite. Some implications of these results for palaeomagnetism are discussed.

Nature of magnetic grains and their effect on the remanent magnetization of basalts

Abstract The nature of magnetic grains in basalts obtained from different parts of the world has been investigated. Results indicate that magnetic behaviour attributable to cation-deficient magnetite is common in basalts younger than Cretaceous, while that due to multidomain magnetite is widespread in much older rocks. Superparamagnetic grains occur in basalts more abundantly than originally presumed, which seem to be mainly responsible for the viscous remanent magnetization of such samples. Basalts which are inferred to contain predominantly optimum single-domain grains are found to be most suitable for palaeomagnetic work. However, many samples generally contain a wide range of grain sizes and this can account for the observed variation in their magnetic stability. One possible mechanism for the formation of such magnetic grains in basalts and its implications to palaeomagnetism is presented. Basalts whose magnetic behaviour is completely reversible on heating and cooling are very rare and because of this fact the reliability of palaeointensity determinations, involving heating of the samples even for one time, may be reduced to a considerable extent.

Ionic etching of titanomagnetite grains in basalts

An etching technique for minerals in rock samples is presented which is based on a bombardment of a mechanically prepolished surface with ionized air. Under certain conditions oxidation of the mineral surfaces can be avoided. The ionic etching enhances the contrast for the study of size and structure of submicroscopic lamellae in exsolved titanomagnetites with both light and electron microscopes. Ionic etching is also a suitable technique for producing stress-free surfaces of natural ferrimagnetic minerals in rocks such as magnetite, titanomagnetite, chromite, goethite and pyrrhotite for the observation of their ferrimagnetic domain configurations.

Ubvri photometry of some lunar topographies

Examples of ‘pure’ lunar mountains, dark and light maria, and cratered terrae have been observed with the UBVRI stellar photometry system. Johnson's (1965) absolute calibration was used to compute brightnesses. These brightnesses were reduced using Hapke's photometric model to a standard geometry (angle of incidence 60°, emergence 40°, phase 90°), and relative albedos were then computed. The mountains, as distinct from the other regions, appear to require a wavelength dependent phase function. The albedos for the four topographic types are approximately linear functions of wavelength. The terrae are redder than the maria. Very low contrast between the topographies is predicted for full-moon at wavelengths shorter than 0.30μ. On the basis of laboratory studies, the lunar particles are comparable to basalt grains having sizes less than 50μm. Larger particle sizes are associated with the dark maria and smaller ones with the cratered highlands.