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tions. The present is in very perfect hexaedral columns, 

 and its yellow varies in intensity, with a greenish and 

 brownish cast. The crystals are soft, brittle, easily scraped 

 with a knife, and the powder* corresponds with the colour 

 of the crystal. The crystals will easily scratch carbonate of 

 lead. Fracture splintery and conchoidal. " Integrant 

 molecule an irregular tetraedron. Primitive form abipyra- 

 midal dodecaedron." — Haiti/. We find these at first, by 

 exposure to the blowpipe, turn green; then they assume a 

 pearly cream colour, and afterwards become irregularly 

 fibrous. The heat being continued, these fibres unite in a 

 somewhat concentrating manner, forming various polygonal 

 facets in an irregular sort of crystallization : see the left 

 hand figure at the bottom. This substance is sometimes 

 situated on an amorphous matrix of its own nature, or on 

 quartz, ochraceous quartz, galaena, &c, as before observed. 



* It is said to be gray by Haiiy, let the colour of the mass be what it 

 will. 



