Ransome.] 



Lawsonite. 



pleochroism, low specific gravity, and comparatively weak double 

 refraction. Although the latter is generally extremely strong in 

 epidote, yet observations show that it may vary between wide limits,* 

 and there seems to be no necessary reason why epidote and zoisite 

 should not show gradations in this respect somewhat comparable 

 with the known gradations in chemical composition. 



The remaining minerals which occur with lawsonite, as con- 

 stituent minerals of the schist, are actinolite, glaucophane, and 

 abundant small red garnets in crystals up to about 3 mm. in diam- 

 eter. These minerals are very variously distributed in different 

 portions of the same mass of schist, so that the latter appears 

 green, blue, yellowish green or red according to the local prepon- 

 derance of actinolite, glaucophane, epidote, or garnet respectively. 

 The glaucophane 'is not deeply colored, the color being rather 

 unevenly distributed, and has the usual pleochroism, light yellow, 

 6 light violet, and c deep sky blue. The relation C : c = 13 — 15 

 was established by means of the quartz wedge, and by reading the 

 extinction angles of sections whose pleochroism showed them to 

 be approximately paralled with the axial plane. The smaller angle 

 given above, which is regarded as being nearest the true one, is 

 twice as great as that given for typical glaucophane, but Hintzef 

 cites similar cases of large extinction angles observed by Schluttig, 

 Koto, and Stelzner. In this case it is probably due to some isomor- 

 phous admixture of the actinolite molecule, and is in full accord 

 with the modern conception, that the minerals of the amphibole 

 group form a continuous series whose members are composed of 

 isomorphous molecules in varying proportions. 



Microscopic sections also show the presence of chlorite and 

 small, highly refracting crystals and grains of titanite. The chlorite 

 is in most cases clearly a decomposition product of garnet. 



Geological Laboratory , 



University of California, May, iScjj. 



*Rosenbusch. Mikroskopische Physiographic, 2d ed., p. 497. 

 t Handbuch der Mineralogie, p. 1258. 



