62 



of which remain with it, and serve to show that the ruder 

 parts have a tendency to the octaedral figure. A remarkable 

 circumstance belonging to this and the green part of the 

 fluor, from Beer Alston, is : that on the hot poker it gives 

 a blue green glow nearly like itself, but lighter from its 

 brightness and somewhat more blue, very nearly resembling 

 the chlorophane of Siberia mentioned at tab. xi. 



The lower representations are designed to show the nature 

 of the crystallization, which at first appears as if it had a rec- 

 tangular octaedron for the primitive and integrant molecule : 

 but on examining the fracture carefully, we find signs of 

 many forms, and can produce fragments truly tetraedral 

 and rhomboidal ; the former of which assists to form the 

 octaedral ; and (vice versa) one octaedron with four tetra- 

 edrons forms a tetraedron placed as in the right-hand figure. 

 An octaedron requires 6 octaedrons and 8 tetraedrons to 

 form it, as in the lowest figure. The rhomb, which might 

 be taken for the primitive, is composed of one octaedron 

 and two tetraedrons, as in the left-hand figure. An octa- 

 edron is tinted in each to make it more apparent, and the 

 lowest figure has also a tetraedron coloured. The fracture 

 "in fluor is very distinct from that of carbonate of 

 lime, and is parallel to the faces of the octaedron, each 

 pkte having always one hexangular face, sometimes 2, 

 forming altogether a flat octaedron, like the bottom half of 

 the left-hand figure in plate xxvi. Perhaps fluor fractures 

 into more natural varieties of figures than any other mineral 



