211 



Fluor. 



In addition to the foregoing, are found crystals in the 

 form of a cube, with its edges replaced by three planes, 

 and also having the additional planes of Fig. 202. PHIL- 

 LIPS describes a crystal in his possession, whose general 

 form is that of a cube, but whose edges are replaced by 

 seven planes, and whose solid angles are replaced by 

 more than four times this number, and resulting in a form 

 bounded by 322 planes. 



Cleavage, parallel with the faces of the regular octahe- 

 dron perfect : rarely also, parallel with the faces of the 

 rhombic dodecahedron and cube. Fracture conchoidal, 

 more or less perfect. 



Surface. The cube generally smooth. Octahedron of- 

 ten rough and drusy. Dodecahedron various, being some- 

 times smooth, at other times rough and drusy. Sometimes 

 the faces of the cube and the tetraconta-octahedrons are 

 curved. 



Lustre vitreous. 



Color white, though not very common, and seldom pure. 

 Generally wine-yellow or violet-blue. Among its brightest 

 colors are emerald and pistachio-green, sky-blue, rose-red, 

 and crimson-red. The dark blue colors bordering upon 

 black, are probably due to bituminous impregnations. Fre- 

 quently different shades of colors are disposed in coats par- 

 allel to the faces of the cube, or symmetrically distributed 

 along the edges or solid angles of crystals. 



Streak white. It is sometimes slightly tinged, if the col- 

 ors be very deep. 



Translucent . . . transparent. Sometimes different colors 

 appear by reflected and by transmitted light. 



Brittle. Hardness =4'0. Sp. gr. = 3*140. 



