i9o6,] SMITH— PARAGENESIS OF MINERALS. 199 



the glaucophane rocks were made, and yet muscovite, paragonite and 

 margarite are abundant, and biotite occurs rarely in the metamor- 

 phics. Muscovite is confined to the acid quartz glaucophane schists, 

 probably made from original orthoclase in the arkose. Paragonite 

 was probably made from the soda of part of the albite molecule 

 when the plagioclase was disintegrated. In the lime rich rocks 

 margarite is abundant, made from the excess of lime of the anor- 

 thite molecule when basic plagioclases were disintegrated. Biotite 

 has probably the same origin as muscovite, with the addition of iron. 



Quartz. — Recrystallized quartz occurs in all the rocks of the 

 glaucophane series, in some forming the greater part of the mass. It 

 was made partly from original quartz in the forms of grains and 

 crystals, but in the diorites it was made from the excess of silica 

 when more basic silicates, such as glaucophane, lawsonite, garnet 

 and epidote, were formed. 



Chlorite. — This is found in many of the rocks as a decomposition 

 product, but in the actinolite schists it seems to be an original 

 product of the recrystallization of basic rocks of the nature of 

 pyroxenites. Actinolite is more acid than the original ferromag- 

 nesian minerals, and the residue would naturally be more basic. 



Talc. — This occurs in large quantities in the lawsonite gneisses 

 and schists. These rocks are made up largely of glaucophane and 

 lawsonite, with crystal plates of talc scattered through them. The 

 glaucophane is perfectly fresh, and there is no other magnesia- 

 bearing mineral that might have given rise to the talc. The original 

 rocks were probably made up of hornblende, or pyroxene and plagio- 

 clase, and the disintegration of the plagioclase molecule furnished cal- 

 cium silicate for the formation of lawsonite, while the albite molecule 

 entered into combination with the hornblende or pyroxene to form 

 glaucophane. The latter mineral requires more silica and less 

 magnesia than the original hornblende or pyroxene, and there is 

 left over an excess of silicate of magnesia, which crystallized out as 

 talc. It is noteworthy that no garnets have been found in the rocks 

 with talc, which shows that the metamorphism has not been so in- 

 tense in this case. 



Other Minerals. — Apatite, magnetite, and pyrite are present in 

 small quantities in most of the glaucophane series, but only the 



PROC. AMER. PHIL. SOC. , XLV. 183M, PRINTED JANUARY 9, I907. 



