104 MINERALOGY AND LITHOLOGY. 
As localities that are of note for black tourmaline, may be noted Graf- 
ton (small, stellated forms of great beauty, and single fine crystals ; com- 
municated by Mr. A. Brown), Sullivan, Unity, Newington, Barrington, 
Bedford, Moosilauke mountain, Hinsdale, Chichester, Goshen, Lyme, 
Moultonborough, Saddleback mountain, White Mountain Notch (very 
large), Monadnock mountain, Surry, and Mt. Kearsarge. Pretty speci- 
mens, formed by needles of black tourmaline piercing white quartz, have 
been found at Hanover, Gilmanton, and Haverhill. A mineral, thought 
to be the kind of hornblende called bentonite, which is found at Leba- 
non, has been shown by Pisani of Paris to be bladed tourmaline. 
The finest tourmalines that are taken from the granitic veins, occur 
in quartz; but the mineral is also found associated with the feldspar and 
mica. When in the mica the crystals are usually flattened out into 
blades, and these blades are often so thin that they are translucent, and 
can be used as polarizers (see p. 85). I think that good specimens for 
the making of a polariscope could be obtained from Grafton. 
The difference of color in tourmalines is much dependent on the 
percentage of iron they contain, which is quite variable. The black 
tourmalines contain much iron, and the brown tourmalines, little. The 
composition of our tourmalines is well illustrated by the two following 
analyses made by Rammelsberg.* The first one is of brown tourmaline 
from Orford, and the second is of the black tourmaline from Unity: 
Silica, . a é 4 : : : a 38.33 36.29 
Boric acid, . 3 a ‘ 5 a 3 5 9.86 9.04 
Alumina, § 4 Fi 5 9 7 a : 33-15 30.44 
Iron protoxide, ‘ ‘ r - : 2.88 13.23 
Magnesia, : é 2 . F ‘ 3 ‘ 10.89 6.32 
Lime, . . . ‘ : x z 5 77. 1.02 
Soda and potash, . : . ‘ : : ; 1.52 1.94 
Water, . . 5 a 3 3 ‘ 3 2.81 1.72 
100,21 100.00 
These analyses agree with the formula given above; and the great dif- 
ference in the amounts of iron contained in the brown and black varieties 
will be noticed. The blue and green varieties, like those at Hinsdale, 
* Handbuch der Mineral Chemie, 1875, p. 541. 
