46 Washington — Study of the Glaucophane Schists. 



the section indicate the decomposition of the specimen, but it 

 is more fresh than the megascopic appearance would indicate. 



" Glaucophane Slate" — The second specimen which was 

 chosen for analysis is one of a rock called by this name by the 

 Japanese geologists. According to Koto* they are extensively 

 developed in the Paleozoic of Japan, and are really " schalsteins," 

 derived from diabase tuffs. The specimen in question, from 

 Kamoi Kotan, Island of Hokkaido (Yesso), is a very fissile, 

 slaty, fine-grained rock, of a general light, blue-gray color, but 

 stained between the folia with limonite. 



Under the microscope it is seen to be very fine-grained, 

 and with the detrital, cataclastic structure of the original 

 diabase tuff very well marked. There are irregular patches of 

 a pale, fibrous glaucophane, with some rather large crystals 

 and fragments of pyroxene, but the greater part is an indeter- 

 minate, very finely granular mass of colorless and yellow 

 grains and fragments, mostly of augite, with some of glass, 

 and possibly of plagioclase. 



The analysis (No. II) resembles the preceding in many 

 respects, but is lower in CaO, and higher in iron oxides, K 2 

 and Ti0 2 .H 2 is high, but no C0 2 was found. 



The analysis, on the whole, confirms the view that the rock 

 is a metamorphosed diabase tuff, and for comparison, analyses 

 of two of these are given in III and IY. 



I. II. III. IV. 



Si0 2 47-89 48-88 47*25 49*13 



A1 2 G 3 13-06 13-44 17-84 14*70 



Fe 2 3 6-77 5-32 5*46 16'40 



FeO 5-36 8-96 7'20 



MgO 4-10 4-21 5-97 4*41 



CaO 11-65 5-80 5'15 9'05 



Na 2 3-35 3*73 2-30 2*96 



K 2 Q 057 171 0-29 1-81 



H 3 OllO°+_. 1-39 3-42) R 



H 2 L10°- ._ 0-12 0-36 \ bi? ° 1-66 



CO, 2-97 none 



Ti0 2 2-14 3-90 inAl 2 3 



MnO_. 0-09 0-14 



99-46 99-73 100*15 100-18 



I. Epidote-glaucophane schist. Norimoto, Yana Distr. Mikawa 

 Prov. Japan. 

 II. " Glaucophane slate." Kamoi Kotan. Isl'd Hokkaido. Japan. 

 III. " Schalstein." Nogurizawa. Kanra Distr. Kozuke Prov. 



Japan. Harada anal. Harada. Die Jap. Inseln., p. 66. 

 IY '"Schalstein." Siebenhitz. NW of Hof. Bavaria. Schwager 

 anal. Giimbel, Geogn. Beschr. Fichtelgeb. 1879, p. 227. 



* Koto, op. cit., p. 89. 



