342 University of California Publications in Geology [Vol. 10 



seldom grouped together and they average one-half centimeter broad 

 and four millimeters thick. A few large ones have been found measur- 

 ing several centimeters in width and thickness. While the basal planes 

 are very brilliant the edges are dull, furrowed and impossible to 

 measure. The thicker crystals show polysynthetic twinning like the 

 micas and extinguish in striated sectors. Thin cleavage plates give a 

 biaxial figure with an apparent optic angle of about twenty degrees. 

 Measurements of the optic angle in sodium light showed a variation 

 from twelve degrees to eighteen degrees. The plane of the optic angle 

 is (100) and the mineral is negative. The refractive indices /3 and y 

 in the basal section are practically the same, determined as 1.660. 



Several analyses of the waluewite from the Urals have been pub- 

 lished and two of them are inserted here for comparison with the 

 Crestmore mineral. 



No. 1. Waluewite from Crestmore. 



No. 2. Waluewite from Slatoust, Urals. Analyzed by Nikolajef.s 

 No. 3. Waluewite from Slatoust, Urals. Analyzed by Clarke and 



Schneider. o 











1 



o 



3 



Si0 2 



16.74% 



16.39% 



16.85% 



Ti0 2 







tr. 



A1A 



42.70 



43.40 



42.33 



Fe,0, 



2.85 



1.57 



2.35 



FeO ' 



0.41 



0.10 



0.20 



CaO 



13.09 



13.04 



13.30 



MgO 



20.03 



20.38 



20.77 



Ign. 



4.49 



4.39 



4.60 





100.31 



99.77 



100.40 



G = 3.081 



Monticellite. — The blue caleite contains monticellite in small masses 

 and grains scattered through it in close association with the waluewite. 

 One large specimen from the quarry consists of a wide band of massive 

 monticellite separated from the blue caleite by a thin seam of walue- 

 wite plates, while the caleite has individual grains and plates, respec- 

 tively, of the two minerals. 



The color of the monticellite is flesh or pale brown and the luster 

 is somewhat greasy. The irregular grains show cleavage faces, but no 

 crystals occur. The mineral is practically infusible and is soluble in 

 acids, forming a gelatinous mass when boiled almost to dryness. 



s Zeitschr. fur Kryst., vol. 9, p. 579, 1885. Abstract. 

 6 Amer. Jour. Sci., vol. 43, p. 379, 1892. 



