Geology topics

Eric Dowty

Publications and source records attributed to Eric Dowty.

4 recordsLinked to original sources

USGS1981

Antiphase domains and reverse thermoremanent magnetism in ilmenite-hematite minerals

Examination of synthetic ilmenite-hematite samples by transmission electron microscopy has for the first time revealed the presence of well-defined antiphase domains and antiphase domain boundaries in this mineral system. Samples quenched from 1300°C have a high density of domain boundaries, whereas samples quenched from 900°C have a much lower density. Only the high-temperature samples acquire reverse thermoremanent magnetism when cooled in an applied magnetic field. The presence of a high density of domain boundaries seems to be a necessary condition for the acquisition of reverse thermoremanent magnetism.

Science↗

USGS1974

Mössbauer spectra of synthetic Ca-Fe pyroxenoids and lunar pyroxferroite

Resolution of the iron sites in the Mössbauer spectra of Ca-Fe pyroxenoids is only partial, two doublets being apparent in each case, whereas there are up to nine cation sites in each structure. Thus the inner and outer doublets represent, respectively: two sites and two sites in Ca 0.5 Fe 0.5 SiO 3 (ferrobustamite); five sites and two sites in Ca 0.15 Fe 0.85 SiO 3 (pyroxferroite); and five sites and four sites in FeSiO 3 (ferrosolite III). Disorder of iron and calcium which exists in the two calcium-bearing pyroxenoids is not readily apparent in the spectra.

Contributions to Mineralogy and Petrology↗

USGS1972

Site distribution of iron in staurolite

The Mössbauer spectrum of staurolite does not necessarily indicate that ferrous iron is distributed over both the tetrahedral Fe site and one or more of the octahedral sites, as previously thought. Two doublets are present in the spectrum, but their quadrupole spliting and isomer shift are more consistent with both being due to tetrahedrally coordinated ferrous iron. Smith's X-ray work has shown that cations in the Fe site actually assume several slightly different positions, and iron in each of these positions may give rise to a different Mössbauer doublet.

Earth and Planetary Science Letters↗

USGS1972

Atomic displacements in ferroelectric trigonal and orthorhombic boracite structures

New crystal-structure refinements of Pca 2 1 boracite, Mg 3 ClB 7 O 13 , and R ϵ c ericaite, Fe 2.4 Mg 0.6 ClB 7 O 13 , show that some boron and oxygen atoms are involved in the ‘ferro’ transitions as well as the metal and halogen atoms. The atomic displacements associated with the polarity changes are as large as 0.6Å.

Solid State Communications↗