Mr. Brooke on Menglte and Sarcolite. 1 89 



terminal edge of the prism is to a lateral edge nearly as 16 

 to 19. Its spec. grav. is 5*1 4. Hardness, between that of 

 apatite and felspar. The colour of the fragments is brownish 

 yellow, that of gadolinite being green. 



Meyigite. 



The mineral I am about to describe I have named after 

 Mr. Menge, who discovered it with the preceding ones near 

 Miask, and whose mineralogical labours have probably not 

 been exceeded by those of any of his contemporaries. 



The Mengite occurs in imbedded crystals in masses of fel- 

 spar and mica in a granitic rock. Its primary form is an 

 oblique rhombic prism, whose terminal and lateral edges are 

 to each other nearly in the ratio of 13 to 18. The planes are 

 too dull for the reflective goniometer, and those of the larger 

 crystals not sufficiently flat to afford very accurate measure- 

 ment by the common goniometer. 



The crystals of this substance present the accompanying 

 figure, the measurements being nearly as follow : 



P,M = 100° 



M,M' = 95 30' 



P,a = 140 30 



P,c = 125 



P,e = 137 30 



The laws of the planes a, 



1 

 are assumed to be O, A, E, G, 



The colour of the crystals is reddish brown. Hardness, 

 between that of apatite and felspar. Spec. grav. 4'88. No 

 regular cleavage. Fracture uneven, and the fractured sur- 

 face dull. It has not been analysed, but from its specific 

 gravity it is probably metallic. It is frequently attached to 

 and penetrated by crystals of Aeschenite, and sometimes of 

 zircon. 



Sarcolite from Vesuvius. 



This mineral appears to have been first observed by Dr. 

 Thomson, who, as Haiiy states, sent some fragments of crystals 

 to liim for examination, from which he inferred that the cube 

 was its primary form, and conjectured that the mineral might 

 be a variety of analcime. Hence red analcinie has been called 

 sarcolite, and the same name has also been given to red 

 gmeliiiite. A specimen, with which I have been favoured by 

 Mr. Hculand, and a fragment of a crystal which 1 liave re- 

 " ceived 



