SUBSILICATES. 283 



composition ; the dark contain much iron and the light 

 colors but little. Some of the varieties have received special 

 names. Rubellite is red tourmaline; and bidicolite, blue and 

 bluish-Mack. 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 contain 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 occur 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 crystals. 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 Edenville, 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. 



