On two Decomposed Varieties of Iolite. 355 | 
same albitic granite in which the chrysoberyl, garnet, columbite, 
zircon, automalite and bismuthic ores occur. A few specimens 
have been observed, in which the pinite assumed a regular crys- 
talline form; the figure of the crystal being either an hexagonal 
prism, or this form altered by the bevelment of its lateral edges. 
The discovery at a more recent date by Prof. Marner, of the 
beautiful blue iolite in the same town, has led to the develop- 
ment of a much greater supply of the pinite; and its occurrence 
is under such conditions as to leave no doubt of its being the first 
mentioned mineral, in a new state of chemical arrangement as 
regards its constituent particles. Both varieties here occur to- 
gether in a large grained, highly crystalline, albitic granite, which 
also abounds in small black tourmalines. The pinite is by far 
the most abundant variety ; good plates of iolite occurring only 
now and then, in limited areas of a foot or two in diameter, while 
the pinite is often so abundant, as mechanically to take the place 
of mica, in the formation of the granite. 
The iolite has frequently been procured here in tabular plates, 
several inches across; and is remarkable for the facility with 
which it admits of cleavage into still thinner layers. This sepa- 
ration is undoubtedly promoted by the presence of exceedingly 
thin plates of what seems to be mica. The crystals are but sel- 
dom possessed of well defined lateral planes, in consequence of the 
a rears. th of mica. albite, tourmaline, and ly 
of tabular spar. When perfect, however, they are either regular 
hexagonal prisms, or else this form, modified by the replacement 
of its. lateral edges. Their color is a rich dark blue, with an oc- 
easional inclination to green; the depth of the color, as is usual 
in.this species, is enhanced by the inspection of the plates ina 
direction perpendicularly to their cleavage. The specific gravity 
of a clear specimen, according to Dr. Tomson, (Outlines of 
Mineralogy and Geology, Vol. 1, p. 278,) is 2:651.. . 2°6643. 
From the same author, we learn that the mineral has the fol- 
lowing composition : 
: Silica, 49.620 
_ Alumina, 28.720 
. Magnesia,, ‘ . “ m * 8.640 
Lime wine aN 0.228 
ae 
eradd Protoxide of iron, . ° . * 11.580 
“ manganese, - a 
