372 PHYSIOGRAPHY. CLASS II. 



Char, of Comb. Henri-prismatic. 



Combination. iJj. -|. (Pr + oo) 5 . (?+ oo) 4 . Pr+ . 



Cleavage, so imperfect, that its direction has not 

 been ascertained. Fracture conchoidal. 



Lustre vitreous, inclining to resinous. Colour 

 greenish-black, very dark. Streak greenish-grey. 

 Translucent on the edges, almost opake. 



Hardness = 6-5 ... 7-0. Sp. Gr. = 4-238. 



Compound Varieties. Massive : composition 

 impalpable, fracture conchoidal. 



OBSERVATIONS. 



1. The above mentioned forms are given on the autho- 

 rity of HAUY, but, according to his own statement, they 

 are only approximations.* 



2. According to BERZELIUS, prismatic Gadolinite con- 

 sists of 



Yttria 45-00. 



Protoxide of Iron 1 1 -43. 



Protoxide of Cerium 17-92. 



Silica 25-80. 



Before the blowpipe it decrepitates, if it has not been 

 heated with the necessary precaution ; and does not melt, 

 except in very small splinters. If heated with precaution 

 upon charcoal, it incandesces at once, and its colour be- 

 comes paler. In nitric acid it loses its colour, and is con- 

 verted into a jelly* 



* Mr PHILLIPS describes an oblique rhombic prism of 115, 

 the terminal plane of which is inclined to the obtuse edge at 

 an angle of 98. It is combined with a horizontal prism of 

 120 in the direction of the short diagonal of the oblique prism, 

 and two faces of a pyramid to which the horizontal prism be- 

 longs, meeting at an angle of 120 ; they replace the obtuse 

 edges of combination in the oblique prism. H> 



