86 



The Sedimentary, Metamorphic, 



Hygroscopic moisture ... 1*67 



Sp. grav. ... ... ... 2756 



Pinite is not a mineral of definite mineral composition. 

 The numerous published analyses show this, while at the 

 same time there is a general resemblance in the percentages 

 given. The microscopical examination of the Ensay mineral 

 shows that it has two varieties of structure : one which is 

 compounded of minute scales, together with larger flakes of 

 a colourless mica; the other somewhat resembles serpen- 

 tine in its " meshed" appearance. Taking this as a basis, the 

 following calculation may be made of the probable con- 

 stituent minerals of this pinite : — 



Molicular Eatio. 



Alkali- 



mica — Si.O„ ... 



... 1-252 







A1. 2 3 



•626 







K 2 



•186 







Na. 2 0. 



•018 







H 3 



•422 

 2-504 



This leaves 



for 



the second constituent of the pinite 



following: — 







Molicular Eatio. 



Si.0 o 









-325 



Fe.O" 









... -093 



Ca.0 









-018 



Mg.O 









-133 



H 2 









-081 



•650 



the 



This calculation very nearly closes, leaving a deficiency of 

 H 2 of -061 Mol., and a surplus of Si.0 2 of '039 Mol. If 

 the interpretation is correct, the second mineral must be a 

 massive talc, and the two minerals would be in the propor- 

 tion of talc to alkali-mica as 1 to 3*85, or about 17 per cent, 

 of the former, to 83 per cent, of the latter. I must, how- 

 ever, point out that, although the sample was collected within 

 the space of a few inches, there was a slight perceptible 

 difference between some of the pieces, showing that even in 

 so short a distance there was probably some slight difference 

 in composition. Either the colour varied in shade, or there 

 was a difference in the completeness of the basal cleavage. 



