NO. 2342. AM E SITE AND CORUNDOPHILITE— SHANNON. 373 



Under the microscope cleavage plates of the amesite are dark in all 

 positions between crossed nicols. Examined in convergent light a 

 black cross is obtanied, which separates slightly on rotation of the 

 stage indicatmg that the mineral is biaxial with the axial angle, 2V, 

 very small, acute bisectrix normal to the perfect cleavage. The 

 optical character is positive. The mineral is colorless as seen under 

 the microscope. The refractive mdices measured by the immersion 

 method were found by Dr. E. S. Larsen to be as follows: 



a=1.597±.003 



/3=1.597±.003 



7=1.612±.003 



a-7= .015 ±.003 



Heated before the blowpipe the amesite swells somewhat and 

 exfoliates slightly becoming silvery brownish white in color. It is 

 infusible. It does not become magnetic when roasted on charcoal. 

 It yields considerable water in the closed tube. The main portion 

 of the water is basic coming off only at a dull red heat. The mineral 

 is partially decomposed by boiling in sulphuric, nitric, or hydrochloric 

 acid with separation of flocculent silica. Upon analysis the pure 

 powder yields the following results: 



Analysis of amesite from Chester, 3fassachv setts. 



SiOj 20. 95 



AI2O3 35. 21 



FeO 8. 28 



CaO 58 



MgO 22. 88 



MnO Trace. 



H2O -110°C 23 



H2O+110°C 13. 02 



Total 101 . 15 



This analysis yields the follov/ing simple ratios: 



Ratios of amesite from Chester, Massachusetts. 



Th is gives the formula — 



2(Fe, Mg) O. AlA- Si02.2H20. 

 or Pisani's formula — 



H,(Mg,Fe)2Al2SiO«. 



This analysis differs from that of Pisa^ii only in the ratio of ferrous 

 ron to magnesia. The definite ratio of MgO : FeO = 5:1 shown by this 



