ALTERATIONS OF NEPHELITE. 293 



Supposing the sodium carbonate to be carried off in solution, the increase 

 in volume would be 24.46 per cent, If two molecules less of water were 

 added, instead of two molecules of gibbsite, two molecules of diaspore 

 would be formed, according to the reaction: 



(3) 6XaAlSi0 4 +5H 2 0+C0 2 =2Na 2 Al 2 H 4 Si 3 12 +2A10(OH)+Na 2 C0 3 +k. 



In this case the increase in volume would be only 15 per cent. 



In the production of thomsonite, calcium must replace the sodium. It 

 will be assumed that this calcium is derived from calcium carbonate. The 

 reaction will then be — 



(4) 6NaAlSi0 4 H-7H 2 0+3CaC0 3 =Ca 3 Al 6 Si 6 M -7H 2 0+3iSfa 2 C0 3 +k. 



Supposing the calcium carbonate to have been brought in solution and the 

 sodium carbonate carried away in solution, the increase in volume is 24.60 

 per cent. 



The less common alteration of nephelite to the zeolite analcite, with 

 the simultaneous production of diaspore or gibbsite, is expressed by the 

 following- reactions: 



(5) 4NaAlSi0 4 +3H 2 0+C0 2 =Na 2 Al 2 Si 4 1 2-2H 2 0+2[A10(OH)]+Na 2 C0 3 +k 

 or 



(6) 4NaAlSi0 4 +5H 2 0+C0 2 =Na 2 A] 2 Si 4 12 .2H 2 0+2Al(OH) 3 +Na 2 C0 3 +k. 



Ill the first case diaspore is simultaneously formed, and in the second case 

 gibbsite. Supposing the sodium carbonate to be carried away in solution 

 the increase in volume is 5.49 per cent if diaspore be formed, and 19.68 

 per cent if gibbsite be formed. 



Alterations of nephelite to muscovite (monoclinic; sp. gr. 2.88), to hydro- 

 muscovite (pinite) (massive; sp. gr. 2.775), and to kaolinite (monoclinic; sp. 

 gr. 2.6-2.63) have also been noticed. Where this alteration takes place 

 the nephelite is probably a potassium-bearing one. Assuming that the 

 amount of potassium is one-third of the sodium, the reaction may be written: 



(7) 2KNa 3 Al 4 Si 4 1G +4H 2 0+3C0. 2 =2KH 2 Al 3 Si 3 12 -|-H 4 Al 2 Si 2 9 -|-3Na 2 C0 3 +k. 



The decrease in volume of the muscovite and kaolin as compared with the 

 nephelite is 16.50, provided the sodium carbonate is carried away in solu- 

 tion. The decrease is 13 per cent if the products are pinite and kaolinite. 

 The volume of the muscovite alone is 38.46 per cent less than that of the 

 nephelite. 



