Chemical Examination of American MineraU. 4o 



our collectors for more than five years, and has a place in 

 most of our cabinets. It has generally been regarded as the 

 fibrolite of Bournon, or a variety of cyanite. Its true na- 

 ture is at length determined. 



12. NACRITE. 



I received this mineral from Dr. Torrey. It was ticketed, 

 Green Mica in Mica-slate, Brunswick, Maine. It consisted 

 of beautiful light-green colored scales, scattered through a 

 mica-slate, composed chiefly of quartz, with abundance of 

 iron pyrites interspersed. 



The color of the scales was partly silvery white, partly a 

 fine white light-green. 



Lustre splendent and silky. 



Very soft. The plates were flexible, but not elastic, and 

 had a good deal of the appearance of talc. 



After ignition they still retained their splendor and silky 

 lustre ; but had lost their green color, and become silvery 

 white. 



The specific gravity was 2'788. 



The constituents were found to be, 



Silica, ------ 64-440 



Alumina, - - _ _ . 28-844 



Peroxide of iron, _ - _ _ 4-428 



Water, - ----- i-ooo 



98-712 



It is obvious, both from the description and the constituents 

 of this mineral, that it is the ialcite of Kirwan, or nacrite of 

 Brongniart. 



There is, doubtless, an excess of silica, owing to the im- 

 possibility of excluding all the quartz grains. Though the 

 scales were picked out one by one, with as much care as pos- 



