Prof. J. P. Cooke on the Vermiculites. 243 



covite mica I send will show the effects I have described with 

 the speciments sent with this. 



Introduction. — In the American Journal of Science, vol. vii. 

 p. 55 (1824), T. H.Webb described a mineral from Millbury, 

 near Worcester, Mass., which has since been a mineralogical 

 curiosity on account of its singular reaction when heated. The 

 mineral consists of " small foliated scales distributed through a 

 steatitic base. . . . When heated, it exfoliates prodigiously, the 

 scales opening out into long worm-like threads made up of the 

 separate laminae. Exfoliation commences at 500° to 600° Fahr., 

 and takes place with so much force as often to break the test- 

 tube in which the mineral may be confined. Before the blow- 

 pipe it fuses at 3*5 to a greyish-black glass." It was named by 

 Webb, as he says, "from the Latin vermiculor, ( I breed worms.' " 

 The hardness of the mineral is 1-2, the specific gravity 2*756, 

 the lustre talcose, and the colour greyish, somewhat brownish. 

 It was analyzed by Crossley, who •"'"separated with great care 

 from the base the scaly mineral, which is the true vermiculite ; n 

 and his results were as follows : — 



Oxygen, Ratio, 

 1. true. app. 



Silica 3574 19*06 1906 11 



Alumina.... 16*42 7*65 7'65 4 



Ferric oxide ... . . . . . , 



Ferrous oxide 10*02 2*23 1 



Magnesia 27*44 10*98 f 



Water 10*30 9*16 9*16 



99*92 



13*21 



Oxygen, Ratio, 



2. true. app. 



35*74 19*06 19*06 2 



16*42 7*65) 10 .oq , 



11*13 3*34 \ luyy l 



27*44 10*98 10*98 1 



10*30 9*16 9*16 I 



101*03 



The results of analysis in column 1, and the portions of the 

 description of the mineral in quotation-marks, above, have been 

 taken from Dana's ' System of Mineralogy/ fifth edition, p. 493 ; 

 and the atomic ratio which is there deduced is 



IV VI II II 



Si:S:R:H = ll:4:7:5. 



In this analysis, however, Crossley could not have determined 

 the state of the iron, which in the specimen I have examined is 

 almost wholly in the ferric condition. If now we assume that 

 the whole of the iron belongs with the sesquioxide radicals, the 

 analysis would appear as in column 2, and the atomic ratio 

 is then seen to be 2 : 1 : 1 : 1, which is undoubtedly the correct 

 result. 



In the year 1851, Mr.W.W. Jefferis, of West Chester, Pa., 

 discovered at the ripidolite locality near that town a peculiar 

 micaceous mineral which exfoliates like the Millbury vermicu- 



K2 



