34 Mr. "William Phillips's Description 



cube in capillary crystals, of which 1 possess a specimen from Tol 

 Carn mine, in recomposed granite, and of the most lively carmine 

 colour. Fig. 32 is an octohedron formed of minute cubes, of which 

 there are several on the same specimen. Fig. S^ shews the passage 

 of the cube into the rhomboidal dodecahedron by the deposition of 

 the cubic facets, progressively diminishing in size, on each face of 

 the cube. This interesting crystal at first excited the suspicion that 

 the cube is the primitive form of the red oxyd, which abated on 

 reflecting that the octohedron will admit a fracture in the direction 

 of its faces, and that the cube will not, as has been already noticed : 

 the direction of the lamina in both cases is shewn by figs. 24 and 37. 

 These circumstances indeed prove the octohedron to be the form of 

 the primitive crystal. 



SECOND modification. 



l^his modification arises from a decrease along the edges of the 

 primitive crystal, which replaces each by a plane perpendicular to 

 the axis that passes through the middle of the edges. It shews the 

 passage of the primitive form into the rhomboidal dodecaedron. 

 The angle formed by the meeting of the face P with the plane 2, 

 Fig. 34, is 144d. 44', 8" as given by Haiiy. The strise on fig. 37, 

 which shews the passage of the primitive form into the rhomboidal 

 dodecaedron, denote the direction of the laminse. In fig. 41, which 

 resembles in its general form the crystallization of the oxyd of tin, 

 the decrease on the edges formed by the meeting of the two pyra- 

 mids is so considerable, as to give the shape of a parallelogram to 

 the four planes which replace the four solid angles, also formed by 

 the meeting of the two pyramids. 



