ORDER vi. PRISMATIC DYSTOME-SPAR. 223 



Lustre vitreous, and particularly in the fracture in- 

 clining to resinous. Colour white inclining to 

 green, yellow, and grey ; sometimes of a dirty 

 olive-green or honey-yellow tinge. Streak white, 

 more or less translucent. 



Brittle. Hardness = 5-0 ... 5-5. Sp. Gr. = 2-989, 

 a variety from Arendal. 



Compound Varieties. Massive : composition 

 granular, of various sizes of individuals ; faces of 

 composition rough and irregularly streaked. 



OBSERVATIONS. 



1. The substance called Botryolito^ is considered by HAUY 

 and others, as a variety of the present species ; while in the 

 system of WERNER, it is considered as a species of its 

 own. It has hitherto been observed only in compound va- 

 rieties of reniform, botryoidal and globular shapes, consist- 

 ing of very thin individuals, which in fact possess ~ome 

 properties, nearly agreeing with those of prismatic Dy*>- 

 tome-spar, but which do not yet allow us to draw any de- 

 cisive inferences, in regard to the determination of the 

 species. 



2. According to KLAPROTH, the simple varieties of Da- 

 tolite, and the compound ones of Botryolite, consist of 



SOica 36-50 36-00. 



Lime 35-50 39-50. 



Boracic Acid 24-00 13-50. 



Oxide of Iron 0-00 1-00. 



Water 4-00 6-50. 



The chemical fomula of the first is Ca B 4 + Ca Si 2 -f 2, 

 Aq, that of the second Ca B 2 + Ca Si 2 + 2 Aq. Exposed 

 to the flame of a candle, it becomes friable. Before the 

 blowpipe it loses its transparency, intumesces and melts 

 into a glassy globule. It is easily soluble in nitric acid 

 and leaves a siliceous gelatine. 



