MINERALOGY. 35 
20. TETRAHEDRITE [Cu, Sb, S,]. 
This mineral, elsewhere so important, is very rare in New Hampshire. 
It has been found in Cornish, associated with stibnite; but the place 
from which the specimens were obtained is now unknown. 
21. FruoritE [Ca Fi,]. 
There are several noteworthy occurrences of fluor spar in our state. At 
the Notch it is found in beautiful sea-green octahedrons, of the size of 
hickory nuts and of perfect form. It occurs in the quartz veins. In the 
more exposed portions of these veins octahedral cavities are found, from 
which the fluor spar has been dissolved, and often these cavities are par- 
tially refilled with quartz, thus showing the process of the formation of 
pseudomorphs by replacement; for, if the process of filling had been 
complete, we should have octahedrons of quartz just like those that come 
from Cornwall. These green octahedrons are found on Mts. Crawford 
and Webster, at Bemis brook, and, indeed, all along the White Mountain 
Notch. Fluor spar forms a vein of considerable size at Westmoreland, 
from which crystals weighing several pounds have been obtained. The 
color is light green, and the crystals are cubic. It is also found at the 
tin mine in Jackson, where crystals of various colors—green, white, and 
purple—are found. A pretty purple variety is found associated with 
albite at Grafton, and also at Newbury. 
Fluor spar, when treated with sulphuric acid, is decomposed with the 
generation of fluor-hydric acid; but if a crystal with bright faces is placed 
in the cold acid for a short time, and then is removed, washed, and exam- 
ined with the microscope, it will be seen that it is not uniformly eaten by 
the acid, but that its surface is covered with little depressions bounded 
by crystallographic faces, which bear a definite relationship to the out- 
lines of the crystal, and are supposed to indicate certain structural lines 
according to which the crystals are built. If, now, one of these green 
octahedral crystals from the Notch is broken so as to obtain a fine 
bright cleavage surface, and is then submitted to the action of sulphuric 
acid, it is etched by the cold acid with the greatest ease, much quicker 
