250 General Notes. 
of their optical axes is the basal pinacoid, and the axial angle, 
measured in oil, is 85° 30’. A is the acute bisectrix. The mineral 
is insoluble in hydrochloric acid. It dissolves slowly in sere, 
sulphuric acid, but rapidly in a mixture of sulphuric an 
hydrochloric acids. An analyses of separated materia 
yielded: Tio, = 46.79%; Fe,0, = 48.64% Mgo = 4.53%. 
Very beautiful rich red, transparent crystals of rhodochrosite are 
described by G. F. Kunz! from the John Reed mine in Alicante, 
Lake co., Colorado. Some of the crystals from this locality “ are 
as pellucid as red Iceland span and show the same double refraction.” 
The same author? describes some curious groups of quartz crystals 
from the vicinity of the town of Pinal, Pinal CO., Arizona. Six 
or more little crystals of the usual form are so arranged as to form 
a hollow cylinder, with the general outline of a large quartz crystal. 
e also mentions a white opaque variety of hydrophane from Colo- 
rado, which is remarkable in that it can absorb more than its own 
volume of water. When wet it is perfectly transparent.—Mr. R. B. 
Riggs’ of the United States Geological Survey has published the 
results of the analyses of a suite of tourmaline crystals from vari- 
ous localities. The conclusions reached by Mr. Riggs, after an 
immense amount of very careful work, are of very great interest as 
establishing with a good deal of accuracy the composition of this 
complicated group of minerals. The figures obtained lead the au- 
thor to regard tourmaline as a simple boro-silicate with the genera 
formula R, Bo, (S i O,),, which for the three types recognized by 
him became : 
I. Lithia tourmaline = 12 SiO, 3B,O, 4H,O. 8Ae¢,0,; 2 
{NaLi),O. 
II. Iron tourmaline = 12 SiO,. 3 B,O,. 4H,o. 7AE,O,. 4 Fe-O. 
Na,O. 
- III. Magnesia tourmaline =.12 SiO, 3B,0,. 4H,O. 5AE,O; 
2% MgO. 3 Na,O 
It is interesting to note that while the color of the iron and mag- 
nésian varieties depends upon the amount of iron in their composi- 
tions, in the case of the lithium varities, containing manganese and 
iron, it depends upon the ratio between the manganese and iron 
constituent, being colorless, pink or pale green when the amounts 
of these are equal, red when manganese is in excess, and green Or 
blue when iron is in larger quantity. 
1 Amer. Jour. Sci., Dec. 1887, p. 477. 
t Ib, D. 479. 
3 Ib., Jan., 1888, p. 35. 
