COMMON ARRAGONITE. 201 The external lustre varies from dull to shining, and is vitrcoUs: internally it is shining and glistening, and vi treous, inclining to resinous. The fracture is foliated, with a fourfold cleavage, in " hich three of the cleavages are parallel with the lateral planes, and the fourth with the terminal planes. The fragments arc indeterminate angular, and rather sharp-edged. It is translucent, passing into semi-transparent, and refracts double. It is semi-hard: it scratches fluor-spar, and even glass, but with difliculty. It is brittle. It is easily frangible. Specific gravity, 2.94115, Hauy. 2.883, 2.928, Karsten. 2.9267, Biot. 2.891, Wiedeman. 2.912, Hour non. Chemical Characters. If we expose a small fragment to the flame of a candle, it almost immediately splits into white particles, which ®re dispersed around the flame. This change takes place principally with fragments of transparent crystals, frag ments of the other varieties becoming merely white and friable. Fragments of calcareous-spar, when placed in a similar situation, undergo no alteration. It is completely soluble, with effervescence, in the ni- frie and muriatic acids. Constituent