106 A. F. Rogers — Lawsonite from California. 



Analyses op Lawsonite 







I 



II 



III 



IV 



V 



VI 













Rocca 















Tiburon, 



Niera, 



Mairatale, 



Arroyo 











Hillebrand 



Italy 



Italy 



Mocho, 



Theory 





Tiburon, 



Tiburon 



& 



Zam- 



Zam- 



Calif. 



H 4 CaAl 2 Si 2 O 10 



Eansome 1 



Palache 1 



Schaller 10 



bonini 11 



bonini 11 



Small 



38-34 



Si0 2 



38-10 



37-32 



38-45 



38-37 



38-21 



38*10 



32-44 



ai,o 3 



28-88 ) 

 0-85 j 



35-14 



31-35 



32-27 



31-98 



32-21 





Fe 2 3 



0-86 



0-23 



tr 



nil 





FeO 









o-io 









nil 





MnO 









tr 











nil 





MgO 



023 







0-17 



0-18 



0-25 



nil 



17-80 



CaO 



18-26 



17*83 



17-52 



18-14 



18-23 



17-74 





Na 2 



0-65 







0-00 



0-36 



n. d. 







K 2 









0-23 



tr 











TiO, 









0-38 











nil" 





co 2 





















1-12 



11-42 



H.O 



11-42 



11-21 



11-21 



11-02 

 100-57 



11-24 



10-85 



100-00 



98-39 



101-50 



100-33 



99-91 



100-02 



essential constituent of schists and gneisses, which usually also 

 contain glaucophane. California, Corsica, Piedmont Alps, and 

 Hantes-Alpes. 



The opinion of J. P. Smith 6 that lawsonite represents the 

 anorthite portion of plagioclase set free in the chemical read- 

 justment incident to metamorphism is well founded. The 

 albite portion of the plagioclase contributes to the formation 

 of glaucophane or at times crystallizes out as albite. 



A dimorphous (isometric) form of H 4 CaAl 2 Si 2 O 10 has been 

 described by Cornu* under the name hibschite. The hib- 

 schite occurs in calcareous inclusions in phonolite at Marien- 

 berg, Bohemia, and has since been found by Lacroixf in cal- 

 careous inclusions of basalt at Ardeche in the Central Plateau, 

 France. 



With these introductory remarks, lawsonite is now described 

 from a number of new localities in the Central Coast Ranges 

 of California ; variation in the habit is especially emphasized. 



Arroyo Mocho, Alameda County. 



In a prominent outcrop of glaucophane schist alongside the 

 road near the head of the Arroyo Mocho and about eighteen 

 miles southeast of Livermore, Alameda County, there were 

 found seams of lawsonite, in part as coarse fibrous masses and 

 in part as distinct crystals in cavities. The lawsonite crystals 



*Min. petr. Mitt., vol. xxv, p. 249, 1906. 



f Mineralogie de la France, vol. iv, p. 705, 1910. 



