of some American Minerals. ! 31 
Brucite, from which it does not differ otherwise than by being 
in a fibrous state. 
Magnesia ` « : : à . 62.89 
Protoxide of iron i 6 i 1 4.65 
Carbonic acid 4 à yA i «5910 
Water (by loss) i à : s 28.36 
100.00 
A small portion of magnesia is replaced by protoxide of 
iron. The formula of Brucite, Mg H, requires, 
Magnesia : ? ; : ‘ ... 09.601 
Water ; ; : ; , t 30.33 
100.00 
Il. CHEMICAL EXAMINATION OF A MINERAL CONTAINING 
OXIDE OF URANIUM, FROM THE NORTH SHORE OF LAKE 
SUPERIOR 
The specimen of which the analysis follows, was given me 
by J. W. Foster, Esq., and is the same mineral which has 
been named Coracite by Mr. J. L. Le Conte, and partially 
. described by him in the Am. Journal of Science (New series, 
Vol. HL. p. 174.) As it is evident that the conclusions drawn 
by: Mr. Le Conte from his qualitative examination, were quite 
incorrect, and as the mineral differs considerably, in its reac- 
tion with acids, from pitchblende, with which it has the great- 
est analogy, and which at first sight it would seem to be, I 
have carefully examined it, with the following results. 
Substance amorphous; fracture uneven; without traces of 
cleavage ; H. 3.; S. G. — ; color pitch-black ; powder grey ; 
lustre resinous. 
Before the blowpipe it does not change its appearance, or 
fuse, or color the flame. It gives with the fluxes the charac- 
teristic reactions of uranium. 
It dissolves readily without the uiia an of heat in dilute 
chlorohydric acid, effervescing strongly ; in which respect it 
differs entirely from pitchblende, which is insoluble, except 
