Arthur Nathaniel Thorpe

Magnetic susceptibility of tektites and some other glasses

Abstract The magnetic susceptibility at several magnetic field strengths of about thirty tektites from various localities have been measured. The susceptibility ranges from 2 × 10−6 to about 7.9 × 10−6 e.m.u./g. Tektites from a given locality have similar susceptibilities. The intensity of magnetization of all the tektites measured is zero or very small. For comparison, the same measurements have been made on about thirty obsidians. The magnetic susceptibilities cover approximately the same range, but the intensity of magnetization of the impurity was found to be much higher. By heating the obsidians to 1450°C the intensity of magnetization was reduced to zero. From the above data, it is shown that the tektites must have been heated well above 1400°C, and that essentially all the iron is in solution. On the other hand, the evidence shows that obsidians have not been heated much above this temperature, and that there is a significant amount of undissolved iron in the glass, probably as magnetite. Further, if tektites are extraterrestrial, they probably entered the earths atmosphere as a glass.

Submicroscopic spherules and color of tektites

Abstract Magnetic susceptibility measurements of 18 tektites from various strewn fields have been made as a function of temperature from 77°K to room temperature. A relatively large temperature-independent component of the magnetic susceptibility was observed in all cases, and an analysis of the data shows that this component is the result of submicroscopic iron spherules in the tektites. An analysis of the color of tektites in terms of the magnetic measurements and also of the optical absorption spectra suggests that the basic color of all tektites is green or greenish-blue, and that the brown to black coloration in some tektites is due to finely dispersed Fe 2 O 3 and/or many metallic spherules, both probably of colloidal size.

Magnetic studies of lunar samples.

The remanent magnetismn of a lunar type C breccia sample includes a large viscous component with a time constant of several hours, and a high coercivity remanence, possibly acquired by impact processes on the lunar surface. Ilmenite(?) and metallic iron in breccias, and ferrous and metallic iron in glass beads separated from lunar fines (type D) were identified by high-field and low-temperature experiments. The iron appears to occur in a wide range of grain sizes including the single domain and multidomain states.

Cell dimensions and antiferromagnetism of lunar and terrestrial ilmenite single crystals

Abstract X-Ray diffraction and anisotropic magnetic measurements have been made on single crystals of lunar ilmenite and on terrestrial ilmenite from Bancroft, Ontario, Canada and the Ilmen Mountains, U.S.S.R. The elongated c -axis of lunar ilmenite, previously reported, is confirmed by new measurements. The shorter c -axis found in terrestrial specimens is ascribed to Fe 3+ substitution for Ti 4+ in the titanium layer. Magnetic measurements on the same specimens show that, in agreement with the Ishikawa-Shirane et al . model, the initial shortening of the c -axis by the above substitution of small amounts of Fe 3+ ( 2+ −Fe 2+ exchange coupling through Fe 3+ in the titanium layer that lowers the Neel transition temperature. The Weiss temperatures and other magnetic parameters confirm this model proposed by Ishikawa and Shirane et al . Additional transitions found in one of the terrestrial specimens (Bancroft) have been ascribed to a small amount of an exsolved spinel phase, possibly a solid solution phase of magnetite-ulvospinel. The spinel phase is localized in hematite-rich blebs which exsolved from the host ilmenite-rich phase.

Comparison of the magnetic properties of glass from Luna 20 with similar properties of glass from the Apollo missions

Abstract Magnetic susceptibility measurements have been made on four glass spherules and fragments from the Luna 20 fines; two at 300°K and two from 300°K to 4°K. From these data the magnetic susceptibility extrapolated to infinite field, the magnetization at low fields and also the saturation magnetization at high fields, the Curie constant, the Weiss temperature, and the temperature-independent susceptibility were determined. Using a model previously proposed for the Apollo specimens, the Curie constant of the antiferromagnetic inclusions and a zero field splitting parameter were calculated for the same specimens. The data show the relatively low concentration of iron in all forms in these specimens. In addition, the Weiss temperature is lower than that measured for the Apollo specimens, and can be attributed almost entirely to the ligand field distortion about the Fe 2+ ions in the glassy phase. The data further suggest that the Luna 20 specimens cooled more slowly than those of the Apollo missions, and that some of the antiferromagnetic inclusions in the glass may have crystallized from the glass during cooling.

Absence of neutral alkali atoms in rhodizite.

The formula CsBl2Be4Al4O28 has been proposed by others for the mineral rhodizite. Electron-spin-resonance and magnetic susceptibility measurements prove the absence of neutral cesium atoms. An ionic formula CsB11Be4Al4O26(OH)2 is proposed.

Magnetic susceptibility and exchange coupling in the mineral ardennite

Abstract Ardennite, a rare silicate mineral, contains about 19 wt.% manganese. Some of the manganese atoms are in positions which are close enough to allow negative exchange and hence a reduction of the total magnetic susceptibility. It is shown that the susceptibility can be accounted for approximately by the treatment of Earnshaw and Lewis (1958) for S = 5 2 and a Hamiltonian H = −2 g μ H b −2 JS 1 · S 2 .