274 Hanks on the occurrence of Durangite in Durango, Mexico. 
zation corresponds to the difference in chemical composition, at 
least so far as these three varieties are concerned. 
cimens from Five Islands, in which the protoxide bases are 
almost wholly made up of soda, the crystal is decidedly rhom- 
bohedral in character; the plane —i is exceedingly minute 
and the basal plane O is wholly wanting. In the Bergen Hill 
crystals which were used in the analyses, and are intermediate 
in composition between the other two, the crystals have not so 
decidedly a rhombohedral appearance, although R and —1 are 
very unequally developed. In the crystals from Two Islands, 
one, but must remain unanswered till specimens containing 
more lime are analyzed and described. 
Art. XXXIV.—On the occurrence of Durangite in the tin-bear- 
ing region of Durango, Mexico; by Henry G. HANKS. 
the last seven years, since the first description appeared in ree 
Journal, I have never been able to obtain anything reliable 
until now. : ee 
It has been stated in a general way, that this rare eee 
was found with stream tin in Durango, Mexico; but as 5 
hardness of durangite is only 5, it has heretofore been ae 
sible to account for the perfect state of the crystals as they 
reach us. : sid 
T am able at last to throw some light on this subject, deriv! ~ 
my information from Mr. J. F d, of Durango, and ™I 
. J. F. Boyd, he 
Ayres, of Coneto, Mexico, both of whom have lately visited San 
¢v 2 Dn 
Francisco. According to these gentlemen, durangite ee 
found only in the “ Barranca” tin mine and never in the about 
streams. The tin fields in which this mine is located “i ae 
eighteen miles northwestwardly from Coneto, State of rae bh 
Mexico, and about ninety miles in the same direction roy 30! 
north, long. 104° 80’ west. The mines are embraced in * ha 
cle which could be swept by a radius of thirteen miles. . 
from ten ' 
In the 
of these arroyos, through all of which water runs during @ sei 
