On two Decomposed Varieties of lolite. 355 



same albitic granite in which the chrysoberyl, garnet, columbite, 

 zircon, automaUte and bismuthic ores occur. A few specimens 

 have been observed, in which the pinite assumed a regular crys- 

 talhne 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. Mather, 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 

 implantation upon them of mica, albite, tourmaline, and more rarely 

 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- 

 casional inclination to green ; the depth of the color, as is usual 

 in this species, is enhanced by the inspection of the plates in a 

 direction perpendicularly to their cleavage. The specific gravity 

 of a clear specimen, according to Dr. Thomson, (Outlines of 

 Mineralogy and Geology, Vol. i, 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, 

 Magnesia, 

 Lime, 



Protoxide of iron, 

 " manganese, 



28.720 

 8.640 

 0.228 



11.580 



1.508 



100.296 



