In a previous paper an account has been given of the composition and properties of a new mineral from Ceylon, chiefly composed of thorium dioxide (78 to 79 per cent.), to which the name thorianite was given. The mineral was shown to contain, besides thoria, a certain proportion of oxides of uranium varying in the three specimens analysed between 11 and 15 per cent., the uranium being present partly as dioxide and partly as trioxide, that is to say, in the same condition as in uraninite or pitchblende. It was shown that the evidence strongly supports the conclusion that thorianite and uraninite possess the same crystalline form and that they are isomorphous minerals. It is interesting to note that the new mineral naëgite, from Japan, which is essentially a silicate of uranium containing thorium, appears to be isomorphous with thorite (thorium silicate). It was suggested that the intimate association of thoria with oxides of uranium in thorianite is to he regarded as a case of isomorphous mixture. Such a mixture, or perhaps “solid solution,” might result from the crystallisation of thorianite from a fused mixture or magma containing the oxides of both elements. We have now obtained important confirmation of this view through the analyses of some unusually large crystalline fragments of thorianite received from the Galle District of Ceylon, which show that a still wider variation may occur in the proportions of the two oxides present in the mineral. This variety is composed of black lumps, usually of indefinite crystalline form, some of the pieces being apparently cubic. They are often partially covered with a brownish yellow substance containing a considerable amount of silica and probably derived from the associated rock. Some of the pieces weighed over 50 grammes, and were evidently portions of much larger masses. The fractured surfaces often showed a slightly less lustrous and more pitchy appearance than ordinary thorianite. The appearance of the mineral is thus intermediate between the small separate and cubical crystals of thorianite and the large masses without definite crystalline form, which are usually characteristic of uraninite. A small amount of material from Hinidumpattu in Galle consisted of small cubic crystal almost indistinguishable in appearance from ordinary thorianite. In hardness, optical properties, density and general physical characters this variety of thorianite closely resembles the ordinary form of the mineral.
Effect of stem crushing on the uniaxial bulk compression behaviour of switchgrass and miscanthus
