Large Laths Research Articles

The evolution of a grospydite from the Roberts Victor mine, South Africa

A grospydite from Roberts Victor contains the most Ca-rich garnets yet found in South African kimberlite xenoliths and also sub-micron sized sodic nepheline in melted and quenched clinopyroxene. Three stages can be recognised in the textural evolution of the grospydite. The first is the development of a layering of large kyanite laths. Kyanite together with complex aluminous clinopyroxene precipitated and accumulated from an evolved residual eclogitic liquid which has penetrated across the garnet join so that garnet no longer precipitated. Solidus conditions for the Roberts Victor grospydite are estimated as T = 1350–1550 ° C, P = 27–39 kbars. Adjacent layers in the grospydite have slightly different mineral compositions suggesting that the small-scale layering (1–5 cm) in this, and associated rocks, may be related to varying activities of R2O3 components and possibly to fo2.

Packet microstructure in Fe-0.2 pct C martensite

The arrangement, size, and boundary area of the laths that make up a packet of martensite in a coarse-grained Fe-0.2 pct C alloy were studied by replica and thin foil electron microscopy. Frequently laths of two habit plane variants coupled to a single {111} A plane of the parent austenite are observed in a packet. The width distribution of the laths is log normal, with the most frequently observed lath width being 0.15 microns. Larger laths between 1 and 2 microns are distributed throughout a packet. The total lath boundary area per unit volume of martensite obtained by analysis of micrographs taken from thin foils is quite high, 65,000 cm-1, and analysis of packet structure by selected area diffraction and precision dark field techniques show that there may be five times as much low angle boundary area as high angle boundary area in a packet.

The micro structure of hydrated super sulphated cement

Mineralogical examination of the setting of super sulphated cement has shown that the rapid increase in strength up to about seven days is due to the formation of large lath like crystals of ettringite, the subsequent but slower increase in strenght is due to the formation of both granular and plate like calcium silicate hydrate.

The isotopic composition of lithium in chondrules

Trace quantities of Li in chondrules from the Bruderheim and Bjurbole meteorites were isolated by chemical procedures that yielded more than 90% of the Li in the sample. The isotopic composition of Li in two samples of Bruderheim chondrules and one sample of Bjurbole chondrules was measured on a 9-inch-radius-of-curvature, single-focusing mass spectrometer. The problem of mass fractionation which occurs during the mass analysis was solved by an integration procedure. The isotopic composition of Li from two samples of ‘whole-rock’ Bruderheim and one sample of the granite G-1 was also measured for comparison. The Li7/Li6 ratios for the chondrules, whole-rock Bruderheim, and G-1 were found to be identical within 3.3% (at the 95% confidence level). The Li content of all the samples was determined by isotope dilution analyses of aliquots of each sample. The contents found were 0.404 ppm for whole-rock Bruderheim, 0.267 ppm for Bruderheim chondrules, 0.089 ppm for a large lath chondrule from Bruderheim, 0.134 ppm for Bjurbole chondrules, and 20.8 ppm for Gr-1. Blanks were less than 0.3% of the sample sizes in our experiments. We are thus unable to confirm a previous report of a 15% excess of Li6 in the Bruderheim meteorite.