54 The American Geologist. '^"'^■' ^^'^-• 
The molecular weioht of the mixture of rare earths. R^O., 
determined by the method indicated above, was found to be, 
249.7. The earths are present in the following percentages : 
I. II. 
Y,0, 4^.c,^ 45.80 
Er.^O;, 1.3-68 13.65 
Gd.jOo 0.42 0.42 
60.03 59-87 
Of course it is just as impossible to obtain a rational form- 
ula from this analysis as from Blomstrand's* very careful 
analyses made with material from Hvalo and Naresto near 
Arendal. 
The small percentage of sulphuric acid found in this material 
from Bandeira de Mello makes it very interesting for it is evi- 
dent that this is a transition product between hussakite and 
xenotime in which onlv a portion of the sulphuric acid has 
been extracted by the circulating waters in nature. During 
this decomposition, other substances as indicated in the analysis 
above, have been deposited in the cracks and pores of the min- 
eral. The crystals of this so called xenotime are of a 
pyramidal habitus, very much rounded and worn and hence 
the faces are dull so that verv accurate measurements could 
not be made ; but nevertheless, it was shown that the angles of 
these crystals agree very closely with those given above for 
hussakite. Inasmuch as the crystals were opaque it was im- 
possible to examine them optically. 
Hence, there seems to be no doul)t but that those xenotime 
crystals, which are opaque and free from sulphuric acid, as 
used for most analyses, are pseudomorphs after transparent 
hussakite. 
As further evidence in proof of this theory, we wish to 
state that we are able to show the presence of sulphuric acid 
in several crystal? from Httero,f which are in the possession 
of the Bavarian ]\Iineralogical Museum in Munich, and which 
Prof. P. Groth kindly placed at our disposal. These crystals 
w'ere partially decomposed, hence in some places opaque, while 
'Blomstrand, Geolog. For. Fcrh., 1887, 9, 185, also Zeitsch. f. Krvstall. 
15, 99. 
*Until now. only one analysis has been made from the xenotime (rotn this 
locality, namely, that by Schicitz. The large percentage of water present 
shows that the material was decomposed and hence all the sulphuric acid had 
doubtlessl3- been extracted in the manner cited above. 
