PHYSIOGRAPHY. 163 



Datholite. 



Cleavage, very indistinct parallel to s, but somewhat 

 more easily observed parallel to P. Fracture uneven, im- 

 perfectly conchoidal. Surfaces, several faces much streak- 

 ed, and others altogether rough. 



Lustre vitreous, and particularly in the fracture inclining 

 to resinous. Color 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 

 rariety from Arendal. 



Compound Varieties. Botryoidal and implanted globu- 

 lar shapes, surface drusy, composition columnar. Mas- 

 sive : composition columnar, consisting of delicate, straight 

 and generally diverging individuals, radiating from a cen- 

 tre ; also granular, of various sizes of individuals, faces of 

 composition rough and irregularly streaked. 



1. Owing to the variation of position in which the crystals of this spe- 

 cies were at first described, they were referred to two different specie*, 

 Datholite and Humboldtite, the latter of which is now abandoned. Still 

 another species or^sub-spccies, according lo some authors, the Botryo- 

 lite, requires also to be united with Datholite. It embraces the reni- 

 fonn and globular shapes, consisting of thin individuals ; but specftnens 

 have lately been discovered, which clearly prove, by transition, their 

 connexion with Datholite. 



> Exposed to the flame of a candle, it becomes friable ; before the blow- 

 pipe, it loses its transparency, intutrjesces, and melts into a glassy glob- 

 ule. It is easily soluble in nitric acid, and leaves a siliceous jelly. 

 2. Analysis. 



By KLAPROTH. 



of crystals. of Botryolite. 



Silica - - S6-50 - - 36-00 



Lime 3550 3950 



Boracic acid - - 24 00 - - - 13-50 



Oxide. of iron - - 0-00 - - - I'OO 



Water - - 400 6-50 



