Vol. 6] 



Eakle: Neocolemanite. 



187 



They vary somewhat from those obtained by Miilheims 7 for 

 colemanite. 



Neocolemanite a = 1.58185; (3 = 1.58746; 7 = 1.60984; .-.2V = 54° 36' 

 Colemanite 1.58626; 1.59202; 1.61398; . -.2V = 54° 52' 



The optic angle measured with sodium light gave for neo- 

 colemanite 



2E = 95° 22'; 2V = 55° 32: 



Chemical composition. — The analysis of the mineral shows 

 that it does not differ from colemanite in composition, so the 

 indicated morphotropy in the vertical direction is not due to a 

 chemical replacement or change. The variety is simply an allo- 

 tropic modification of colemanite brought about by a possible 

 difference in the mode of crystallization. 



In the analysis of the neocolemanite the boric oxide was 

 determined by titration with standard sodium hydrate, using 

 mannite to set free the boron. The calcium was determined 

 both gravimetrically and volumetrically. 



Analysis : 



B,0 3 49.45% 



CaO 27.76 



H 2 22.48 



99.69 



Specific gravity = 2.423 at 13° C. 



HOWLITE 



Occurrence. — The silico-borate of lime occurs in considerable 

 quantity in the deposit, as large and small nodular masses em- 

 bedded in the layers of the lime borate. The mineral is very 

 compact with a fine flaky structure and a snow-white color. 

 Black streaks of carbonaceous matter ramify through much of 

 the compact round masses. The layers of neocolemanite are bent 

 and curved around the knotty lumps of howlite, which appear 

 like "Augen" in the banded borate. The surfaces of some of 

 the nodules have a botryoidal structure, but no crystals have 

 been found. 



i A. Mulheims. Colemanit von Californien. Zeitschr. fur Kryst., 14 

 (1888), 230. 



