SCAPOLITE GROUP. 311 



The volume decrease of the actinolite and spinels as compared with the 

 olivine and feldspar is 7.18 per cent. 



The reactions in the alterations of olivine into tremolite are parallel 

 with those for actinolite, with the exception that no iron is present, and the 

 mineral therefore probably forms from forsterite. The reaction may be 

 written : 



( 8 ) 3Mg 2 Si0 4 +2CaC0 3 +5Si0 2 =2Mg 3 CaSi 4 12 +2C0 2 - k. 



The decrease in volume of the tremolite as compared with the forsterite, 

 calcite, and silica is 12.29 per cent. 



The alteration of olivine to serpentine and the accompanying minerals 

 is the common one. It takes place in the zone of katamorphism on a great 

 scale, both in the belt of weathering and in the belt of cementation. Corre- 

 sponding with the position in the upper jjhysical-chemical zone, the reactions 

 occur with hydration, oxidation, expansion of volume, and liberation of heat. 



The developments of anthophyllite, actinolite, and tremolite from 

 olivine and actinolite, and of spinel from olivine and feldspar, are all deep- 

 seated reactions of the zone of anamorphism. Corresponding to this position 

 the change to anthophyllite, equation (5), is a reaction of silication; the 

 changes to actinolite and to tremolite, equations (6) and (8), silication 

 and decarbonation ; and the change of olivine and anorthite to actinolite 

 and spinel, equation (7), rearrangement of the silicates into denser silicates; 

 and all take place with diminution of volume and absorption of heat. 



SCAPOLITE GROUP. 

 MEIONITE, tVEKXERITE, and 5IARIALITE. 



The scapolite group includes: 



Meionite: 



Ca 4 Al 6 Si 6 25 - 



Tetragonal. 



Sp. gr. 2.70-2.74. 



Wernerite: 



mNa 4 Al 3 Si 9 24 Cl.nCa 4 Al 6 Si 6 O 25 . 



Tetragonal. 



Sp. gr. 2.66-2.73. 



Marialite: 



Na 4 Al 3 Si 9 24 Cl. 

 Tetragonal . 

 Sp. gr. 2.566. 



