The physical properties of the metamict minerals are discussed and tabulated. Because of their isotropy and the variability of the index of refraction of these minerals, the petrographic microscope has limited value for their identification. Ordinarily, x-ray diffraction yields little additional information. Heating of certain specimens, however, induces some crystallinity in many of these “amorphous” minerals. A technique was developed for treating the metamict minerals to facilitate their systematic study for purposes of identification. Data are given for metamict zircon, thorite and uranothorite, euxenite, brannerite, fergusonite, samarskite, davidite, and allanite.*
It is also observed that some of the “more stable” related minerals that ordinarily occur in the crystalline state are structurally changed when subjected to temperatures at which many of the metamict minerals crystallize. This may indicate that the crystallized (by heating) metamict material is not reconstituted to the original crystal structure.