112 A. F. Rogers — Lawsonite from California. 



clase is cloudy but shows albite twinning. Measurements 

 of the extinction angle indicate that it is andesine, about 

 A^An^ Irregularly distributed through the feldspar are 

 small, elongated lawsonite crystals with parallel extinction, 

 bright interference-colors, and elongation parallel to the fast 

 ray. From a study of the cross-sections it is evident that the 

 lawsonite crystals have a habit similar to tig. 3. This rock is 

 only slightly altered and we have here the beginning of saus- 

 suritization of the feldspars. This is an excellent example of 

 the chemical readjustment as explained by J. P. Smith. 8 The 

 soda end of the plagioclase forms glaucophane while the lime 

 end forms lawsonite. 



Slightly altered igneous rocks of this type seem to be rather 

 common in the Mt. Hamilton region. J. P. Smith 8 mentions 

 a quartz-diorite from Oak Ridge, Santa Clara County, in which 

 the original minerals are oligoclase, katophorite-like horn- 

 blende, and quartz. The secondary minerals are lawsonite 

 and crossite. 



Lawsonite-glaucophan e Schists. 



In addition to the localities mentioned in this paper and by 

 J. P. Smith 8 in his valuable paper on the glaucophane-bearing 

 rocks, I have studied lawsonite-bearing glaucophane-schists 

 from the following localities : 



Hubbard Ranch, Isabel Creek, Santa Clara Co. Isabel Val- 

 ley, Santa Clara Co. L'Ecuyer's Panch, Arroyo Mocho, Ala- 

 meda Co. Southern end of Tesla topographic sheet, Alameda 

 Co. Cedar Mountain, Alameda Co. Yager, Humboldt Co. 

 (collected by Mr. W. G-. Cooper). 



Thelen 12 also mentions lawsonite as a constituent of the 

 glaucophane schists of North Berkeley, California. 



Bibliography of Lawsonite. 



1. Eansome, Bull. Dept. Geol., Univ. of California Pub., vol. i, p. 301, 

 1895. 



2. Palache and Ransome, Zs. Kr., vol. xxv, p. 351, 1896. 



3. Franchi, Bull. Soc. Fr. Min., vol. xx. p. 5, 1897. 



4. Viola, Zs. Kr., vol. xxviii, p. 553, 1897. 



5. Lacroix, Bull. Soc. Fr. Min., vol. xx, 309, 1897. 



6. Manasss, Memroie Soc. Toscana di Scienze Naturali in Pisa, vol. xx, 

 p. 19, 1903. 



7. Termier, Bull. Soc. Fr. Min., vol. xxvii, p. 265, 1904. 



8. Smith, Proc. Am. Phil. Soc, vol. xlv, p. 183, 1907. 



9. Eakle, Bull. Dept. Geol., Univ. California Pub., vol. v, p. 81, 1907. 



10. Hillebrand and Schaller, this Journal (4), vol. xvii, p. 195, 1904. 



11. Zambonini, Rendic. R. Accad. Lincei, Rom., 2 Sem., 1904 (5), vol. 

 xiii, p. 466. Abstr. Zs. Kr., vol. xlii, p. 60. 



12. Thelen, Bull. Dept. Geol., Univ. of California Pub., vol. iv, p, 221, 

 1905. 



13. Murgoci, Bull. Dept. Geol., Univ. of California Pub., vol. iv, p. 359, 

 1906. 



Stanford University, California, Jan., 1914. 



