i9o6] SMITH— PARAGENESIS OF MINERALS. 227 



its soda to form glaucophane, and setting free the anorthite mole- 

 cule, CaAloSisOg which by taking up water becomes lawsonite, 

 CaAlgSigOg + 2H0O. When this has taken place little epidote was 

 formed, and usually no garnets, although in the rock from which 

 lawsonite was first described both garnet and epidote are abundant. 



As evidence that the metamorphism that produced the uralite 

 and pargasite rocks was not so fundamental as that which formed 

 the glaucophane, it may be stated that the pargasite rocks are more 

 massive, and not true schists, and that in these rocks the glaucophane 

 appears as replacements or rims around the pargasite. Alost of the 

 schistosity has been produced after the glaucophane was formed, for 

 even that mineral is usually bent and fractured, the cracks being 

 healed w^th secondary silica, forming quartz veins which occur as 

 innumerable small seams through these rocks. 



No original micas of any sort are found in the gabbros and 

 medium basic diorites of the Coast Ranges, and yet the eclogites, 

 glaucophane schists and gneisses are full of white mica, chiefly the 

 sodium-bearing paragonite and the lime-bearing margarite. These 

 are formed at the expense of the plagioclases, either by their giving 

 up silica and alkali-silicate, or by their taking up alumina from 

 aluminous silicates. The reactions given below show how the micas 

 may have been formed. 



3KAlSi308 (orthoclase) -^ HoO^-KoSiOg -f sSiOs 



-f HoKAl3(SiOj3 (muscovite). 

 KAlSisOg + AI2O3 + H20 = HJ<:Al3(SiOj3 (muscovite). 

 3NaAlSi308 (albite) -f H.O = Na^SiOs + sSiO, 



+ H2NaAl3( 5104)3 (paragonite). 

 NaAlSisOg + AUO3 + HoO = H2NaAl3(SiOj3 (paragonite). ^'"^^^ 

 y^o 2CaAl2Si208 (anorthite) + U.O = CaSi03^-f SiOs 

 ^p-^ \c^l . +rt^HSi20i2 (margarite). 



CaAl^Si^Os (anorthite) -fAU03 + H,0 '^ (X«^vC^cj>4',.C 



^<; f =HoCaAl4SioOio (margarite). 



Neither albite nor anorthite occurs in the original igneous rocks 

 from which these metamorphics were made, but the albite and the 

 anorthite molecule are both abundant in the plagioclases which 

 made up a large portion of those rocks. All three of these micas 



