BORACITE. 263 The external surface is generally rough, seldom smooth, when it is shining or splendent, and adamantine.^ Internally the lustre is shining, inclining to glistening, and is adamantine, inclining to resinous. The fracture is intermediate between small and fine grained uneven and imperfect conchoidal, sometimes con cealed foliated, with a threefold cleavage, the folia paral lel with the sides of the cube. The fragments are indeterminate angular, and not par ticularly sharp-edged. It is sometimes translucent, sometimes transparent. It is scmi-hard in a high degree; it scratches glass. It is brittle. It is easily frangible. Specific gravity, 2.5663, Wcstrumb. 2.911, Karslen. Physical Characters. It is pyro-electric on all the angles, those that are dia gonally opposite being one positive, and the other nega tive. Chemical Characters. llefore the blowpipe, it is fusible, with ebullition, into a yellowish enamel. Constituent Parts. From Luneburg. From Srgebcrg. From Luneburg. I-imc, 11.00 Magnesia, 13.50 36.3 16.6 Alumina, 1.00 Silica, 2.00 flxide of Iron, 0.75 Iloracic Acid, 68.00 63.7 83.4 96.25 100 100.0 irestmai. rj4- Vauquelin. 4 Vauquelin
