Identity of Edwardsite with Monazite. 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. Brooxe 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. 
Brooxe 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. xxxu, 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 ate very conspicuous in it, 
in exact accordance with those which are so striking in the 
American mineral. 
