SUBSILICATES. 283 
composition ; the dark contain much iron and the light 
colors but little. Some of the varieties have received special 
names. Rudbellite is red tourmaline; and Indicolite, blue and 
bluish-black. Schorl formerly included the common black 
tourmaline, but the name is not now used. 
The presence of boron trioxide is the most remarkable 
point in the constitution of this mineral. The colorless, red, 
and pale-greenish kinds usually conta lithia. B.B. the 
darker varieties fuse with ease, and the lighter with difficulty. 
On mixing the powdered mineral with potassium bisulphate 
and fluor spar, and heating B.B., gives a green flame owing . 
- to the boron. 
Diff. The black and the dark varieties generally, are 
readily distinguished by the form and lustre and absence of 
distinct cleavage, together with their difficult fusibility. 
The black when fractured often appear a little like a black 
resin. ‘The brown variety resembles garnet or idocrase, but 
is more infusible. The red, green, and yellow varieties are 
distinguished from any species they resemble by the crystal- 
line form, the prisms of tourmaline always having 3, 6, 9, 
or 12 prismatic sides (or some multiple of 3). The electric 
properties of the crystals, when heated, is another remarka- 
ble character of this mineral. The test for boron is always 
good. | 
Obs. Tourmalines are common in granite, gneiss, mica 
schist, chlorite schist, steatite, and granular limestone. 
They usually oceur penetrating the rock. The black crys- 
tals are often highly polished and at times a foot in length, 
when perhaps of no larger dimensions than a pipe-stem, or 
even more slender. This mineral has also been observed in 
sandstones near basaltic or trap dikes. 
Red and green tourmalines, over an inch in diameter and 
transparent, have been obtained at Paris and Hebron, Me., 
besides pink and blue erystals. These several varieties oc- 
cur also, of less beauty, at Chesterfield and Goshen, Mass. 
Good black tourmalines are found at Norwich, New Brain- 
tree, and Carlisle, Mass. ; Alsted, Acworth, and Saddleback 
Mountain, N. H.; Haddam and Monroe, Conn. ; Sara- 
toga and Hdenville, N. Y. ; Franklin and Newton, N. J.; 
near Unionville, Chester, and Middletown, Penn. ;.trans- 
parent brown at Hunterstown, Canada East ; amber-colored 
at Fitzroy; black at Bathurst, and Elmsley, Canada West ; 
fine greenish yellow at G. Calumet I. 
