(5) Summary: 1. The radio-active lode-stuff of Radium Hill, near Olary, South Australia, is a mineral complex consisting of an intimate admixture of ilmenite, magnetite, rutile, carnotite, and a mineral which is probably a titanate or silico-titanate of rare earths, etc., and which may possibly prove to be tscheffkinite or some allied mineral. The predominant constituent is ilmenite, the other minerals being present as impregnations.

2. The carnotite, which occurs sparingly in cracks and cavities, partly as a yellow powder and partly in the form of minute, tabular crystals and platy aggregates, is entirely and definitely crystalline, the crystals belonging to the orthorhombic system. The physical characters, taken in conjunction with the chemical composition, indicate that carnotite is a definite mineral, belonging to the uranite group, and that it may be regarded as the vanadium analogue of autunite.

3. The Colorado carnotite, though not so definite in its crystalline condition as the Australian mineral, contains tabular crystals and platy aggregates which are orthorhombic in symmetry; and it is probable that these are mineralogically identical with those of the Australian carnotite.

4. The supposed new minerals ‘davidite’ and ‘sefströmite’ are apparently identical with the complex above referred to.