| Analysis gives | Silex from | 35 to 58 |
| Alumine | 20 to 48 | |
| Magnesia | 0 to 10 | |
| Iron | 0 to 23 | |
| Manganese | 0 to 13 | |
| Alkali | 0 to 10 | |
| Water | 0 to 4 |
These differences must be in some measure ascribed to a defect in the accuracy of some of the analyses. But it appears that iron has not been discovered in the red tourmaline. It is not unworthy of notice, that the red tourmaline is considered as infusible, but the others fusible.
The red tourmaline has been the most valued, from its scarcity, its employment in jewelry, and the beauty of its crystals. It has been discovered in Siberia, in Moravia, in the East-Indies, and in Massachusetts. In Siberia it is found in a vein of decomposed feldspar in a fine-grained granite, with black tourmaline. In Moravia with quartz and lepidolite (or rose-coloured mica) in gneiss. In the East-Indies, at Ava and Ceylon, but its geological situation is not known, though it is probably in gneiss or granite.
The red or rose tourmaline of Massachusetts, is found chiefly at Chesterfield, in a subordinate bed of granite, contained in mica slate. The mica slate is the predominant rock of the country. It is fine grained, and contains an abundance of small garnets. Direction of the strata north and south, varying a little easterly; inclination perpendicular. The bed of granite is about three hundred feet long, and from five to twenty feet broad. It is contained in a narrow ridge of mica slate, which descends into, and is lost in, a valley. The sides are precipitous; the highest part is about forty feet high. On the east side a considerable part of the granite has been destroyed by natural causes, leaving the granite bare. The granite consists chiefly of granular feldspar, with grains of white quartz, and a little light coloured mica, is moderately fine grained, and of a grayish white colour. In addition to tourmaline, it contains also emerald, some of the crystals of which are from three to five inches in diameter. I succeeded in getting one out of its matrix, which is three and a half inches in diameter, and its summit (which is a plane without any additional facettes) is perfect.
The tourmalines are contained chiefly in a false vein of silicious feldspar and quartz, which begins in the centre of the upper edge of the bed of granite, and passes obliquely, descending to the northeast, about twenty feet, where it is intercepted from sight by the mica slate. The vein is about one and a half foot thick in the upper part, and not more than six or eight inches where it is lost. This vein of silicious feldspar contains also a vein of bluish white transparent quartz, which is from three to eight inches thick, and passes through the centre of the vein of feldspar.
When I first examined this rock, soon after its discovery by Dr. Hunt, of Northampton, I determined the feldspar to be a new variety, which has been since confirmed by Professor Hauffman, and now ranks as a new sub-species, under the name of silicious feldspar. (P. 41, of the Mineralogical Table.)
The analysis of Professor Stromeyer, of Gottingen, gives,
| Silex | 70.68 |
| Alumine | 19.80 |
| Soda | 9.05 |
| Iron, Mag. and Lime | .38 |
| —— | |
| 99.91 |