e 
Gibbs. on Tourmalines, §c. 
~~ 
The analysis of Professor. Stromeyer; of Gottingen, gives, 
via. iene 1OBBe bog 
Silex. t43-te-< 
_ Alumine-. -. ~-. -; 19.80 
Soda, +220 ob: tee: 9.06 
Iron, Mag. and Lime, . 38 
99.91 
“The chief difference between this and the tere is, that 
one contains fourteen potash and the other nine soda, Be- 
tween this and the saussurite, or tenaceous feldspar, the one 
contains eleven of lime, and the other only a trace. 
The silicious feldspar, which I suspect to he the basis of the 
granite crystallizes in thin rhomboidal tables. They are very 
frangible, and have one cleavage perpendicular to the faces of 
the tables. Sometimes the tables have one lateral edge or 
more, truncated. In one fragment of a crystal I observed a 
very obtuse acumination on the table, which appeared to be 
diedral, the sides being placed on the obtuse lateral edges of 
the tables. On account of the extreme frangibility of the 
crystals, it is certainly extremely difficult to seize their char- 
acters. Specific gravity only 2.335, probably owing to inter- 
' stices between the tables. The color is white, translucid, 
passing to semi-transparent; lustre sometimes dull, at others 
shining, The tables are sometimes so aggregated that their 
edges being exposed, offer wedge-shaped and stelliform figures. 
The tourmalines are chiefly contained in this vein. They are 
red, or green, rarely blue or black. 
The green tourmalines vary from one-eighth of an inch to 
Oe inch in diameter; they are sometimes four inches in 
length, and are entirely confined to the inner vein of quartz. 
They are triedral prisms, with convex faces, striated longi- 
tudinally, and generally traversed perpendicularly to the axis, 
With yery small fissures filled by some silicious substance, 
Probably feldspar. These green crystals are opaque. The 
Ted tourmaline is frequently enclosed in the green. In certain 
Parts of the vein almost every green crystal encloses a re 
one, which always corresponds by its sides and angles. with 
Vol. No. 4 
