The energetics and structure of the hydrogarnet defect in grossular: A computer simulation study

We have used computer simulation methods to model the structure and energetics of the hydrogarnet defect in grossular. The predicted structure is in good agreement with experimental data. The calculated energy for the reaction of water with grossular to form the hydrogarnet defect is 1.02 Ev (98 kJ mol^-1). This low energy of reaction suggests that such defects will be common in garnets where they could play an important role in effecting processes such as atomic transport.     

A direct measurement of the distribution in depth of 26Al in the Estacado meteorite

The two-dimensional distribution of ²⁶Al across a slice of the Estacado meteorite was measured using non-destructive γ-γ coincidence counting. The maximum activity was found to be 60 ± 2 dpm kg^?1 and the variation across the slice rather small. The intensity and distribution are in moderate agreement with existing theoretical models if the pre-atmospheric shape of the meteorite had been a sphere of radius 0.35 ± 0.05 m, but it was more likely to have been slightly non-spherical.     

Frequency distribution of zinc concentrations in the common mussel,Mytilus edulis (L.)

The frequency distribution of zinc concentrations in a population of mussels (Mytilus edulis) from the moderately polluted Tyne estuary showed marked positive skewness. A peak was reached between 3 and 4 μmoles per dry gram of whole soft tissue followed by a long tail ending with a single exceptional value of 20.5 μmoles per g. The mean zinc concentration for the population was 5.13±2.66 (standard deviation). The skewness (g¹) value was 1.78 (SE+0.14 p?0.001). Within the population, there was a strong positive association between the log mean zinc concentration of a single collection and the log variance of the collection. The significance of this for biomonitoring procedures is discussed.     

Foraminiferids from the London Clay at Lower Swanwick and their palaeoecological interpretation

Sixteen foraminiferid assemblages have been studied from the London Clay succession at Lower Swanwick brickyard. These are divided into three faunules which are interpreted as indicating a shallow shelf regime with strong deltaic influences.     

Re-interpretation of a mixed petrographic province — The Sintra intrusive complex (Portugal) and related rocks

Sub-alkaline to calc-alkaline granite dominates the high-level plutonic massif of the Serra de Sintra, while two overlapping ring complexes recognised within it consist of four distinct alkaline to sub-alkaline quartz-bearing syenitic units, together with intrusions of a remarkable kaersutite- and (titan?)biotite-bearing theralite heteromorph (Mafraite), contaminated to varying degrees by sialic admixture. Large volumes of sub-volcanic breccia testify to considerable late explosive activity in and near the ring centres. Minor intrusives are approximate compositional counterparts of the plutonic rocks, but more closely resemble lavas forming the extensive “basaltic mantle” of the Lisbon region, where compositions range from olivine basalt, basanite and theralite (luscladite) to subordinate quartz-bearing trachyandesite and trachyte. Undersaturated salic rocks are absent throughout the province. Magmatic differentiation probably played a minimal part in petrogenesis of the Sintra intrusives. The granite is interpreted as a direct product of basement syntexis, the other rocks as products of selective palingenetic reactions between mafraitic magma and crystalline basement (or granite). Evolution of the volcanic and hypabyssal rocks may have been controlled by similar reactions, but evidence favouring differentiation of this suite from sialcontaminated basic parents is almost as strong. There are some points of resemblance between this province and that of the Auvergne region in southern France.     

Studies of the formation process of water-in-oil emulsions

This paper summarizes studies to determine the formation process of water-in-oil emulsions and the stability of such emulsions formed in the laboratory and in a large test tank. These studies have confirmed that water-in-oil mixtures can be grouped into four states: stable emulsions, unstable water-in-oil mixtures, mesostable emulsions, and entrained water. These states are differentiated by rheological properties as well as by differences in visual appearance. The viscosity of a stable emulsion at a shear rate of one reciprocal second is about three orders of magnitude greater than that of the starting oil. An unstable emulsion usually has a viscosity no more than about 20 times greater than that of the starting oil. A stable emulsion has a significant elasticity, whereas an unstable emulsion does not. A mesostable emulsion has properties between stable and unstable, but breaks down within a few days of standing. The usual situation is that emulsions are either obviously stable, mesostable, or unstable. Entrained water, water suspended in oil by viscous forces alone, is also evident. Very few emulsions have questionable stability. Analytical techniques were developed to test these observations.

The type of emulsion produced is determined primarily by the properties of the starting oil. The most important of these properties are the asphaltene and resin content and the viscosity of the oil. The composition and property ranges of the starting oil that would be required to form each of the water-in-oil states are discussed in this paper.