550 TUNGSTEN, OR SCHEELIUM. 3. When the truncating planes in Fig. 271. become so large as to obliterate the original planes, there j is formed an oblique four-sided prism, which is acuminated with four planes, set on the lateral planes, and the summits bevelled, as in Fig 272*. 4. Rectangular four-sided table, in which the two j opposite lateral planes are bevelled, and the j angles truncated. The crystals are middle sized and large, and occur im bedded, or intersecting one another, but are seldom di stinct. The lateral planes are usually longitudinally streaked ( and glistening. ; The principal fracture is shining or splendent; the cross fracture is glistening; the lustre is metallic, inclin, ing to adamantine. The principal fracture is foliated ; with a distinct cleav age in the direction of the smaller lateral planes of the prism, and a less distinct one at right angles to the form er, and parallel with the larger planes. The cross fracture is coarse and small-grained uneven. The fragments are indeterminate angular, and blunt- edged. It seldom occurs in angulo-granular or prismatic con cretions; more frequently in thick or thin lamellar con cretions ; which are either fortifications wise bent, or con- j centrically curved, and in which the surfaces are trans versely streaked. It is opaque. It yields a dark reddish-brown coloured streak. It * Scheelin ferrugine progressif, Haujr* 4