The feldspar phenocrysts of some British and Icelandic Tertiary acid glasses have been studied optically and chemically. Six new analyses of the feldspar phenocrysts are presented together with an anorthoclase from a glassy pantellerite. The analysed feldspars and all the other feldspar phenocrysts that have been examined show high-temperature optics, and confirm the results of previous investigations of plagioclase feldspar determinative curves. The relationship of the feldspar phenoerysts to the plagioclase components in the analysed residual glasses conforms to the synthetic plagioelase system, and the crystallization of feldspar in natural acid melts is considered.

Calcite is widespread in amygdales associated with the zeolites; the characteristic forms being and a steep scalenohedron in the zone , usually . Crystals from one locality have faces of , a form new to calcite.

The first scientific examination of the Dalgaranga crater has revealed specimens exhibiting a variety of structures and compositions hitherto unknown in connexion with any meteorite crater. Excavations have yielded much-weathered specimens and permitted measurements of the form and depth of the original pit. The question of age is considered, and the impacting meteorite is thought to have been largely stony but at least in part a mesosiderite.

Evidence is presented for the existence of silicon-oxygen chains up to 1000 Å. in length in melts of CaMgSi2O6 and of LiAISi2O6 at temperatures a little above the melting point.

From thermodynamic considerations of the system anorthite-åkermanite it appears that the melts in this system are ionic in nature. The liquidus relation in this system would thus seem to afford confirmation of the theory, based on conductivity measurements, that silicate melts such as molten anorthite dissociate into such ions as Ca2+ and (Al2Si2O8)2−.

Further thermodynamic calculations involving no unreasonable assumption lead to a close reproduction of the experimental liquidus curve of åkermanite. This lends added strength to the belief in the stable existence of åkermanite down to the eutectic; no evidence in support of the claim that åkermanes becomes unstable below 1 325° C. (Osborn and Schairer, 1941) was encountered.

According to Osborn et al. (1954) the presence of substantial Ca2+ increases the desulphurizing potential of blast furnace slag. The thermodynamic treatment of the binary system anorthite-åkermanite leads to the conclusion that both phases dissociate in the molten state and in mutual solution to yield Ca2+; it therefore appears probable that a high concentration of these minerals in the slag would have a salutary effect on the slag chemistry.

An unusual monazite deposit of metasomatic origin is described. The monazite occurs as randomly oriented crystals in a dolomitic marble. The chemical composition and optical data of the monazite are given.

Uraninite from Geevor Mine, Cornwall, has been analysed by the complete lead method and an age of 290±7 million years has been accepted. Similar studies of uranium from Tyndrum Mine, Perthshire, give an age of 230±8 million years. The significance of the results is briefly considered.

An examination of available chemical analyses shows that the anthophyllite and cummingtonite series of amphibole minerals are not isodimorphous. Whilst the anthophyllites are truly lime-free amphiboles, small amounts of calcium are essential to stabilize the monoclinic lattice of cummingtonites, which should be regarded as lime-poor amphiboles, analogous to the lime-poor pyroxenes. The existence of synthetic clino-anthophyllites is considered.