SPINEL. £9 times inclines to duck-blue, which is nearly allied to green : on the other side it passes from crimson-red into blood-red, and hyacinth-red, into a colour intermediate between orange and ochre yellow, into yellowish-brown, and reddish brown. From the cochineal-red it passes through rose-red into reddish-white. The colours are seldom pure, being generally somewhat muddy. The blue and white varieties are rare, and the green variety is Very rare. It occurs, sometimes in grains, more frequently crys tallised. The grains are usually rolled crystals. The following are its crystallizations: 1. Perfect octahedron, which is the fundamental fi gure. Fig. 13. 2. Octahedron, with alternate larger and smaller planes. 3. Tetrahedron, slightly truncated on the angles. Fig. 14. 4. Perfect tetrahedron. Fig. 15. 5. Tetrahedron, deeply truncated on the apex. 0. Segment of figure 3. 7. Two segments of the tetrahedron, truncated on the angles, as in figure 3. joined together in a con formable manner by their bases, forming a twin- crystal with three re-entering angles. 8. Two segments of the tetrahedron, truncated on the angles, (as in figure 3.), joined together by theLt bases in an unconformable manner, so that the ex tremities of the segments project. Twin-crystal. 9. Two crystals, N u 5. attached by their bases. Twin- crystal. Fig. 1 ti. 10. A crystal of N° 6. attached by its base to the la teral plane of a crystal N° 5. 'Twin-crystal. 11. A crystal of N® 10. attached to one of N u 13. I riple-crystal. 12. Octahedron, in which two opposite planes are much larger than the others. 11. A v