SAPPHIRE IN UNITED STATES. 118 
nf shafts and open cuts, the limestone making fairly firm walls. By 
hydraulic processes the decomposed rock was readily broken up and 
\vashed into sluice boxes. As the mining extended deeper the rock 
\\ as much less altered, and it was necessary to leave a great deal of it 
exposed to the atmosphere from one season to the next before it could 
I >e broken up and run through the sluice boxes. At a number of points 
I he almost perfectly fresh rock has been encountered, and from this 
it will be a difficult problem to separate the sapphires. The per- 
centage of sapphires in the rock is small, and if it were the unaltered 
lock that had to be worked for them the deposit would not be of 
<c()nomic importance. This dike as exposed in the main workings of 
the mine is illustrated in PL VII, 5, which shows the brecciated 
character of the dike, as described. 
The sapphires occur embedded in this rock in distinct crystals from 
less than a millimeter in diameter to some that were over 15 mm. 
Their color, as far as I have observed them, is always a blue, varying 
I'rom light blue to a very few that showed the dark blue of the Ceylon 
-tone. The prevailing color is a bright blue.^^ 
Although the color of these sapphires is not as dark as the highly 
prized Ceylon and Siam stones, they show a richness and brillianc^y 
not equaled by the oriental stone. They not only show a strong, rich 
color by transmitted light, but their color is almost as good by 
reflected light. Then, again, although many blue sapphires make 
beautiful day stones, but are dull at night, the Yogo sapphire is very 
brilliant at night as well as in the day. 
The crystallography of these sapphires is markedly different from 
that of the sapphires of the Missouri River and Rock Creek (j). 
109). The latter all show a prismatic development, while the former 
are all rhombohedral crystals, none of which show the presence of any 
prism face.^ 
The crystals are etched and striated to such a degree that no crys- 
tallographic measurements on the reflecting goniometer were pos- 
sible; but sufficiently accurate angles were obtained with the contact 
goniometer to permit the identification of the faces. The only two 
faces that could be identified were the base c (0001) and the rhombo- 
hedron x (3032), which is a new face for corundum. On one crystal 
two very small faces were observed, which were too small to be 
measured with the contact goniometer, but were probably the faces of 
a pyramid of the second order. 
In determining the rhombohedron, ten or more independent meas- 
urements were made of c/\x. These varied from 66° to 68°, but 
Kunz, O. F.. Am. Jour. Sci., 4th ser., vol. 4. 1897, p. 420. 
Am. Jour. Sci.. Uh ser., vol. 4, 1897, p. 424. 
Bull. 2G9— 06 M- 
