Vol. 5] 



Eakle. — Columbite. 



87 



A cursory examination of some of the crystalline schists of 

 California, collected by G. D. Louderback, shows the presence of 

 the same tabular crystals of lawsonite in specimens from differ- 

 ent localities. Professor Louderback, who is making a detailed 

 petrographieal study of these rocks, states that thin sections of 

 many of his specimens contain lawsonite which is not macroscop- 

 ically visible. 



Conclusion. — All of these observations prove conclusively that 

 lawsonite has an extended distribution in the State of California. 

 The mineral is generally considered as rare, but petrographically 

 it cannot be so held, and in regions of dynamic metamorphism, 

 whether glaucophane is formed or not, it may be expected. Com- 

 paratively little attention has been directed to it as a rock con- 

 stituent, and this perhaps accounts for its omission from the list 

 of metamorphic minerals by Van Hise in his excellent "Treatise 

 on Metamorphism." 11 Rosenbusch in his new edition of the 

 ' ' Mikroscopische Physiographie, ' ' and Weinschenk in his ' ' Ges- 

 teinbildene Mineralien" accord it proper recognition as a rock 

 constituent. 



The natural habitat of lawsonite seems to be in regions of 

 glaucophanitic rocks, although glaucophane is not always directly 

 associated with it. The opinion prevails that it is a product of 

 the metamorphism of the soda lime feldspars of the basic rocks, 

 the soda entering into the formation of glaucophane while the 

 lime goes to lawsonite, which is analogous to anorthite with two 

 molecules of water. Its similarity in formation to zoisite and epi- 

 dote leads to the belief that it may occur in rocks outside of glau- 

 cophanitic provinces. 



COLUMBITE. 



Introduction. — San Diego County has become widely known 

 through its deposit of rubellite-tourmaline in lepidotite at Mesa 

 Grande, specimens of which have been sent to all parts of the 

 world and are recognized as distinctly characteristic of this local- 

 ity. More recently mines have been opened at Pala which pro- 

 duce i'ose and green tourmalines which equal any found in Maine, 

 Siberia, or Brazil. The newest find of a gem mineral is the beau- 



11 Monograph XLVII, 1904, U. S. Geol. Survey. 



