296 A TREATISE ON METAMORPHISM. 



zeolites, diaspore (orthorhombic ; sp. gr., 3.3-3.5) or gibbsite (monoclinic ; 

 sp. gr., 2.3-2.4) is frequently formed. 



In' the production of hydronephelite the reaction is — 



(1) 2(NaC1.3NaAlSi0 4 )+4H 2 0+C0 2 =2HNa 2 Al 3 Si 3 12 .3H 2 0+2NaCl+Na 2 C0 3 +k. 



Supposing that the sodium chloride and sodium carbonate are dissolved, 

 the decrease in volume is 7.25 per cent. 



In the alteration of socialite to natrolite, gibbsite or diaspore is also 

 produced The reaction, provided gibbsite .be produced, is — 



(2) 2(NaC1.3NaAlSi0 4 )+7H 2 0+C0 2 =2Na 2 Al 2 H 4 Si 3 12 +2Al(OH) 3 +2]S T aCl+Na 2 C03+k. 



If two molecules less of water were added, in place of the gibbsite two 

 molecules of diaspore would be produced, according to the reaction: 



(3) 2(NaC1.3NaAlSiO i )i-5H 2 0+C0 2 =2Na 2 Al 2 H 4 Si 3 12 +2A10(OH)+2NaCl+Na 2 C0 3 +k. 



Supposing the sodium chloride and sodium carbonate to be dissolved, 

 the decrease in volume in the first case would be 6.52 per cent, and in the 

 second case 13.62 per cent. 



In the production of thomsonite the reaction is — 



(4) 2(NaC1.3NaAlSi0 4 )+7H 2 0+3CaC0 3 =Ca 3 Al 6 Si 6 24 .7H 2 0+2NaCl-f-3Na 2 C0 3 +k. 



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

 chloride and sodium carbonate to be taken into solution, the decrease in 

 volume is 6.41 per cent. 



The alteration of socialite to aualcite and to diaspore may be written 

 as follows: 



(5) 4(NaC1.3NaAlSi0 4 ) +9H 2 0+3C0 2 = 



■ 3(Na 2 Al 2 Si 4 12 .2H 2 0)+6A10(OH)+4NaCl+3(Na,CO s ) +k. 



If six additional molecules of water were added, as in the case of the 

 reaction written for natrolite, gibbsite instead of diaspore would be formed. 

 The reaction is — 



(6) 4(NaC1.3NaAlSi0 4 )+15H 2 0+3C0 2 = 



3(Na 2 Al 2 Si 4 12 .2H 2 0)+6Al(OH) 3 +4NaCl+3Na 2 C0 3 +k. 



Supposing the sodium chloride and sodium carbonate to be taken into 

 solution, the decrease in volume is 20.77 per cent in the case of diaspore 

 and 10.11 per cent in the case of gibbsite. 



