ANNALS 



or 



PHILOSOPHY. 



APRIL, 1823. 



Article I. 



Description of a mw Mineral By Mr. A. Levy, MA. of the 



University of Paris. 



(To the Editor of the Annals of Philosophy.) 



SIR, Great liusscll-strcct, Bloomsbi/ry, March 3, 1823. 



I shall again beg the favour of your inserting in the Annals 

 of Philosophy the crystallographical description of a mineral 

 which I cannot refer to any substance whose primary form has 

 been determined hitherto. It occurs in small brilliant yellowish- 

 brown crystals, with adularia and lamellary crichtonite, and 

 comes from Dauphiny. On account of its colour, accompani- 

 ment, and locality, it has been classed with sphene ; but as it 

 will appear from what follows, it differs essentially from this last 

 substance. Its hardness is much less than that of sphene ; it 

 cleaves very easily in one direction, and the face of cleavage is 

 perfectly brilliant. The primary 

 form is an oblique rhombic prism, 

 fig. 1, in which the incidence of 

 the two lateral planes in, m, is 

 90° 10', that of the base p on one 

 of the lateral planes 99° 40', and 

 the ratio between one side of the 

 base and one of the lateral edges 

 nearly that of 10 to 7. The pri- 

 mary form of sphene is also an 

 oblique rhombic prism, but its 

 dimensions are different. The 

 incidence of the two lateral 



New Series, vol. v. r 



Fig. 1. 



