Chemical Examination of American Minerals. Go 



Silica, - 36-00 



Alumina, -_-___- 17.50 



Magnesia, ------- 2*52 



Lime, ___-__- o7-G5 



Peroxide of iron, -.---- 5-25 



Lime, a trace, ------ 0'36 



99-28 



This analysis shows clearly, that gokumite and Loboite are 

 two different minerals. 



20. IDOCRASE. 



This mineral was sent me by Dr. Torrey, with the label, 

 a new varitty of garnet (idocrase <f some) from Salisbwy, 

 Connecticvt. I have givt^n it the name of idocrase, from the 

 result of its chemical analysis. 



The color is brownish-red, very similar to that of some 

 garnets. 



The fracture is granular, and when the specimen is exam- 

 ined by a microscope, it appears to ccuisist of a conaeries of 

 prismatic crystals, some of which exhibit a brilliant facet or 

 two ; but the slape cannot be made out. In another speci- 

 men the extremities of four-sided prisms, apparently square, 

 are distinctly visible, though the faces are too rough and 

 uneven to admit of measurement, even with the common go- 

 niometer. 



Scratched with difficulty by the knife, but easily by quartz. 



Lustre shining, glassy. 



Brittle. Easily frangible in the great ; but the individual 

 crystals are rather tough. 



Specific gravity 3*503. 



The constituents were found to be. 



