8. _Prothéeïte—a new Mineral_.—This mineral was discovered in 1826, at Rothenkoph, in the valley of Zillerthal, Tyrol. It occurs in rectangular prisms, generally without distinct summits, and rough at both ends. The angles are very seldom truncated, the faces are striated longitudinally. The crystals are of various sizes, some being very small, but they have occurred 5 inches in length, and two in width; the longitudinal fracture is lamellar, the cross-fracture conchoidal. The substance is usually fissured, nearly opaque in large specimens, translucent or diaphanous in small masses. Its colour is crysolite green or white, or between the two; its lustre between that of glass and the diamond; it is heavy; a good conductor of heat; hard enough to scratch glass; infusible before the blowpipe; highly electric by friction. The white crystals have a fibrous texture, which, as well as the colour, seems the result of decomposition. When cut and polished, the mineral assumes a great variety of aspects; the green parts then resemble the finest crysolites, but the fibrous white parts, when cut of a round form, present one or two reflections on a transparent ground which move as the stone is moved, just like those from the cat’s eye; these reflections are very brilliant, and are accompanied by numerous iris colours, which move like those on the opal. This phenomenon is often observed in the rough stone, which, when exposed to light, exhibit certain deep red tints of a cupreous colour, and metallic lustre on all the faces.—_Bull. Univ._ B. xi. 42.