116' COPPER. intermediate between the octahedron and the rhomboidal or garnet dodecahedron. 4. Rhomboidal or garnet dodecahedron. 5. Twin-crystal, resembling that of the spinel, which is formed by the union of two segments of deeply truncated tetrahedrons, joined base to base, so that the conjoined truncatures form three re-en tering angles, and the lateral planes three salient angles. The crystals are usually small and very small, and ge nerally ■ superimposed. Externally it is intermediate between glistening and shining, and is often splendent. Internally it is shining, which in some varieties passes into glimmering, and the lustre is metallic. The fracture is most commonly coarse and small-grain ed uneven : the coarse-grained passes on the one hand in to imperfect and small conchoidal, and from this into im perfect foliated : the small-grained passes into fine-grain ed uneven, and into even, and large and flat conchoidal. The lustre varies with the fracture ; the foliated has the strongest lustre, and its colour approaches to gold-yellow: the next in intensity of lustre is the small conchoidal: and the laige conchoidal and even, have the least lustre, being only glimmering. It sometimes occurs in curved lamellar concretions. The fragments are indeterminate angular, and rather sharp-edged. It is intermediate between semi-hard and soft. It is brittle. It is easily frangible. It is heavy. " Specific gravity, 4.1 GO, Gcllcrt. 4.080, Kir man. 4.344, BrUson. 4.3154, Ilauy. Chemical