334 A TREATISE ON METAMORPHISM. 



(9) stilbite alters into albite, and (10) into orthoclase; (11) chabazite 

 alters into natrolite (hexagonal-rhombohedral (Hintze), orthorhombic 

 (Dana); sp. gr. 2.225); (12) laumontite alters into albite, (13) into ortho- 

 clase and prehnite, and (14) into analcite (isometric; sp. gr. 2.255). 



These alterations may be expressed by the following equations, the 

 numbers of the equations corresponding to the numbers of the alterations. 

 In writing these equations, whether Groth's or Clarke's formula is used 

 depends on which is more nearly analogous to the formula of the mineral 

 produced. 



(1) Na 2 Al 2 Si3O 10 .2H 2 O+2CaCO 3 =H 2 Ca 2 Al,Si3O 12 +Na. 2 CO3-|-CO 2 +H 2 O-k. 



(2) H 2 Na 2 CaAl 4 Si 6 21 .4H 2 0+3CaC03=2H 2 Ca 2 Al 2 Si 3 12 +Na. 2 C0 3 +2C0 2 +3H 2 0-k. 



(3) H 2 CaAl 2 Si 3 O n .2H 2 0+CaC0 3 =H 2 Ca 2 Al 2 Si 3 12 +2H 2 0+C0 2 --k. 



(4) Na 2 Al 2 Si 4 I2 .2H 2 04-2Si0 2 =2NaAlSi 3 8 +2H 2 0-k. 



(5) 3(Na 2 Al,Si 4 12 .2H 2 0)+4CaC0 3 + K 2 C0 3 = 



2KAlSi 3 O s +2H 2 Ca 2 Al 2 Si 3 12 -j-3Na. i C0 3 +2C0 2 +4H,0— k. 



(6) H 14 Ca 4 Si 6 23 +Na 2 C0 3 =2HNaCa. 2 Si 3 9 +6H 2 0+C0 2 -k. 



(7) H 4 CaAl 2 Si 6 18 .3H 2 0+Na 2 C0 3 =2NaAlSi 3 8 +CaC0 3 4-5H 2 0-k. 



(8) H 4 CaAl 2 Si 6 18 .3H 2 0+K 2 C0 3 =2KAlSi 3 O b + CaC0 3 +5H 2 0-k. 



(9) Ca 3 Al G Si 18 J8 .18H 2 0+3JSra 2 C0 3 =6NaAlSi30 8 -|-3CaC03+18H 2 0— k. 



(10) Ca 3 Al 6 Si 15 48 .18H,0+3K 2 C<.) 3 =6KAlSi 3 O s +3CaC0 3 +18H 2 0~k. 



(11) Ca 3 Al 6 Si 12 36 .lSH 2 0+2Al(OH) 3 +4Na. 2 C0 3 = 



4H 1 Xa,Al 2 Si 3 12 --3CaC0 3 +C0 2 +13H 2 0-k. 



(12) Ca 3 Al 6 Si 12 36 .12H 2 0+2]S T a 2 C0 3 +C0 2 =4NaAlSi 3 8 +Al,0 3 +3CaC0 3 -(-12H 2 0-k. 



(13) Ca 3 Al 6 Si 12 36 .12H 2 0+CaC0 3 +K 2 C0 3 = 



2KAlSi 3 O 8 +2H 2 Ca 2 Al 2 Si 3 O 12 +2CO 2 +10H 2 O-k. 



(14) Ca 3 Al 6 Si 12 36 .12H 2 0+3Na 2 C03=3(Na 2 Al 2 Si 4 Oi2-2H 2 0)+30aC03i-6H 2 0-k. 



The decreases in volumes are as follows: Prehnite as compared with 

 the natrolite, equation (1), 16.12 per cent; prehnite as compared with meso- 

 lite, equation (2), 15.05 per cent; prehnite as compared with scolecite, 

 equation (3), 16.66 per cent; albite as compared with the analcite and 

 quartz, equation (4), 17.25 per cent; orthoclase and prehnite as compared 

 with analcite, equation (5), 14.09 per cent; pectolite as compared with 

 apophyllite, equation (6), 19.48 per cent; albite as compared with heulan- 

 dite, equation (7), 25.03 per cent; orthoclase as compared with heulandite, 

 equation (8), 18.44 per cent; albite as compared with stilbite, equation (9), 

 31.67 per cent; orthoclase as compared with stilbite, equation (10), 25.66 

 per cent; natrolite as compared with chabazite, equation (11), 4.58 per 



