.548 tungsten, or scheelium. passes into yellowish-grey, and light yellowish brown, which approaches to orange-yellow. The white varieties are sometimes tarnished on the surface, either dark pearl-grey or plum-blue. It occurs massive, disseminated, and crystallised in tlie following figures: 1. Acute octahedron *, fig. 267. in which the edges of the common base are 130° 20'. This figure is sometimes truncated on the lateral edges, and on the summits. When the truncations on the lateral edges become so large as to cause the original faces to disappear, then there is formed S. A less acute octahedron f, in which the edges on the common base are 113° 36', and those form ed by the meeting of the lateral planes 107® 26'; which is sometimes truncated on the summits’ or flatly acupiinated on the summits with four planes, which are set on the lateral planes, a* in fig. 268. This octahedron is sometimes so deep ly truncated on the summits, that there is form ed 3. A four-sided table, in which the terminal planes are bevelled, as in fig. 269. In this figure the lateral planes correspond to the truncating planes of the octahedron, and the bevelling,,lanes to the lateral planes of the octahedron. • Sometimes the angles formed by the meeting of an 1 ^ n *' nat ‘ n 8 planes, fig. 269. are truncated, 6 tru »cating planes set on the lateral edges. The * Scheelin calcairc primitif, Many, t Scheelin calcaire unitaiie, Hauy.