Identity of Edwardsite with Mojiazite. 251 



" The chief differences then are that Monazite contains both 

 oxide of cerium and lanthanium, the Edwardsite only peroxide of 

 cerium, (Shepard gives protoxide,) that the former contains tho- 

 rina, the latter zirconia. Lanthanium is probably contained in 

 Edwardsite, as it generally accompanies cerium, having been first 

 discovered during the past year by Mosander, (was unknown to 

 Shepard.) In regard to thorina and zirconia, it can hardly be 

 assumed that the given quantities are correct, since we have no 

 accurate method of separating them from oxide of cerium ; it is 

 nevertheless, worthy of notice that 7.77 zirconia are a nearly full 

 equivalent for 17.95 thorina, for the former contains 2.04, the 

 thorina 2. 12 oxygen. It might, therefore, be supposed that the 

 thorina is replaced by zirconia in Edwardsite, which, however, 

 cannot be assumed from the present view of their atomic compo- 

 sition, since, according to Berzelius, thorina is expressed by Th 

 + 0, zirconia by 2 Zr + 30. The tin in Monazite is evidently 

 accidental from its minuteness ; but remarkably enough, as Rose 

 remarks, he found it also in Edwardsite, by means of the blow- 

 pipe. If the presence of zirconia in Edwardsite be confirmed, 

 and its isomorphy with thorina, then these two minerals can only 

 be separated as species : if not, then both will probably agree in 

 their chemical composition ; in which case, it will be more proper 

 to retain the name Monazite, which it first received." 



It is proper in the first place to observe that Monazite is the 

 same mineral as that described by Mr. H. J. Brooke under the 

 name of Mengite in the Philosophical Magazine and Annals for 

 Sept. 1831, (p. 189.) Having received from this gentleman a good 

 crystal of the Uralian mineral, and being very forcibly struck by 

 the considerations presented in the foregoing paper, I instantly set 

 about such an examination of the Edwardsite as the nature of the 

 case solicited at my hands. 



Their identity in crystalline form appears to be nearly complete. 

 Brooke gives M on M 95° 30', and I find the crystals of Ed- 

 wardsite to measure from 95° to 95° 30^ Again his angle be- 

 tween the base (P) and the prism (M) corresponds exactly with 

 mine, as given in my first paper on the Edwardsite. (See this 

 Journal, Vol. xxxii, p. 162.) Being unwilling to fracture my crys- 

 tal of Monazite to learn its cleavages, I can only add on this head 

 that lines, or rifts of diagonal cleavage are very conspicuous in it, 

 in exact accordance with those which are so striking in the 

 American mineral. 



