OllDER vi. DIATOMOUS KOUPHONE-SPAR. 235 



3. ?f. If. P -f oo. Pr + x. Huelgoet, 



Brittany. 



Cleavage, Pr + GO distinct ; traces of Pr + oo. 

 Fracture uneven, scarcely observable. Surface, 



?r 



either smooth or uneven. The faces parallel 



2 



to the principal axis striated in that direction. 



Lustre vitreous, inclining to pearly upon the more 

 distinct faces of cleavage. Colour white, pass- 

 ing into some reddish, yellowish, or greyish tints. 

 Streak white. Translucent. 



Not very brittle. Hardness unknown. Sp. Gr. = 

 2-3, HAUY. 



Compound Varieties. Massive : composition gra- 

 nular, commonly elongated in one direction, faces 

 of composition generally streaked. 



OBSERVATIONS. 



1. According to two analyses, one by L. GMELIN, and 

 another by VOGEL, the present species consists of 



Silica 48-30 49-00. 



Alumina 22-70 22-00. 



Lime 12-10 0-00. 



Water 16-00 17'50. 



Carbonic Acid 0-00 2-50. 



Before the blowpipe it gives the same results as the pre- 

 ceding species. It gelatinises with acids, and acquires neg- 

 ative electricity by friction, if isolated. It is decomposed 

 by the action of the atmosphere, and loses its water ; it is 

 therefore generally met with in a friable state, and most of 

 its properties are on that account but imperfectly known. 



2. It occurs in veins traversing clay-slate, with rhombo- 



