Phillips on Mineralogy . 



325 



Mon M 120 00 



PonMorM 90 00 



/or A 90 00 



M on h 120 00 



d 1 118 12 



or M or/ 1 50 00 



Pon C I 



144. 1 

 153 45 

 90 00 

 101 50 

 103 42 

 112 45 



It is found on Somma, with brownish mica. 



The letters on each plane of the larger figure are placed accord- 

 ing to the system of notation adoipted by Mr. Brookes in his Fami- 

 liar Introduction to Crystallography, of which we propose to give 

 our readers an account in our next number. In the mean time 

 we fully agree with Mr. Phillips in " recommending it strongly to 

 the student, as being calculated to teach the interesting science on 

 which it treats in its most pleasing form;" and we will add, as 

 ably as pleasantly. 



We should do our author injustice, if we were not to mention 

 that the verbal description of the Humite is much shorter than the 

 generaUty of the descriptions contained in the work. The hardness, 

 specific gravity, chemical composition, and the principal characters 

 of each substance before the blow-pipe, are, in most cases, care- 

 fully stated ; and that they have been omitted in the description of 

 Humite, is owing, we conclude, partly to its scarcity, and partly 

 because it occurs only in minute, and, usually, separate crystals, 

 wherefore the two first characters are hardly attainable, and we are 

 not aware that any accurate analysis of this mineral has hitherto 

 been made. 



As only one plane of cleavage has yet been noticed, the primary 

 form has necessarily been deduced from the nature and direction 

 of the secondary planes, which, although perfectly consistent with 

 the right rhombic prism, (the primary form adopted by Mr. Phil- 

 lips,) are equally compatible with the assumption of a right rect-N 

 angular prism for the primary form, in which case P, /, and h, 

 would be the primary planes. 



The utility of connecting the primary and secondary forms, as 

 is done in a variety of instances throughout the work, is obvious ; 

 and a little attentive consideration will convince the observer of 

 the manner in which the various secondary planes are allied to the 

 primary crystal. Thus in the figure annexed, the planes/ replace 

 the obtuse lateral edges of the prism, and incline equally on M and 

 M ; the planes h, in like manner, replace the acute lateral edges ; 



