38 Pen field and Stanley — 



The ratios are not bad in the first three analyses, but in the 

 last two they are unsatisfactory and, moreover, in analysis V 

 there is not sufficient fluorine and hydroxy! to satisfy the last 

 assumption. The burden of proof rests with the more exact 

 ratios as given on page 36, and the assumption that the sesqui- 

 oxides enter the metasilicate molecule as bivalent radicals 

 corresponding to [R/'^IFOH),]'". 



It is interesting to note to what extent the hydrogen atoms 

 of the amphibole acid are replaced. According to the long- 

 accepted' formula for tremolite, Mg 3 CaSi 4 12 , three-quarters, or 

 75 per cent, are replaced by Mg and the remaining quarter by 

 Ca, while in actinolite the isomorphous Fe,. Mn and Mg together 

 have been regarded as replacing three-quarters of the hydro- 

 gens. The replacement, expressed in per cents, as they appear 

 in the analyses, are as follows: 



I 



Fe + Mn + Mg]" 65-2 



Ca + K, + Na„|" 25-8 



R 2 "'0(F,OH) 2 ]" T5* 



H 2 in excess of (OH) 6-9 



Ca alone 24*0 



It may be seen from the foregoing table that (Fe+Mn + Mg) 

 never make up 75 per cent of the total hydrogen replacement, 

 and that the figures are remarkably constant at about 65 per 

 cent. Ca alone never replaces 25 per cent of the total hydro- 

 gens, but if there are added to the Ca the small amounts of 

 alkali metals present, K 2 and Na 2 , the near approach to 25 per 

 cent is remarkable ; in analysis II, where Ca alone is low, the 

 deficiency is made up by a rather high percentage of l^a 2 

 (2*15^), while in the remaining analyses it ranged frem 0*19 to 

 0*82, averaging - 54$. In all cases K 2 was low, ranging from 

 0*22 to 0*54 and averaging 0*33^. The trivalent elements, Al 

 and Fe, presumably entering into the amphibole molecule as 

 bivalent fluor-hydroxyl radicals, are quite variable, and so also 

 are the amounts of hydrogen in excess of that required in each 

 analysis for combination as hydroxyl with Al and Fe. 



Edenite — Pargasite — Hornblende. 



The name edenite has been employed to designate light- 

 colored varieties of amphibole containing considerable alumina. 

 Chemically there are analogous dark-colored varieties some- 

 times called pargasite, containing high percentages of iron, 

 and both kinds doubtless grade imperceptibly into one another 



II 



III 





IV 





V 



64-2 



65-5 





63-2 





64-8 



25-7 



23-7 





25-5 





26-1 



1-9 



1-8 





45 





6-7 



8-2 



9-0 





6-8 





2-4 



24-7 



23-1 





23*8 





21-6 



n the 



analysis. 



Se 



e page 



50. 





