446 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



The optical properties as determined by Dr. E. S. Larsen are as 

 follows : 

 Indices of refraction : 



a=1.665, ±.003. 



/3=1.673, ±.003. 



7=1.682, ±.003. 



a— 7= .017, ±.003. 



Optically positive ( + ). 2V, near 90°. Pleochroism distinct: a=pale reddish 



brown ; ;8=nearly colorless ; 7=very pale reddish brown. 



The indices of refraction are considerably higher than are those 

 of the Nevada material, the indices of which were found to be as 

 follows: a=1.650; ^=1.660; y=1.672. 



This suggests that a gradual increase in the indices of refraction 

 accompanies the replacement of manganese by iron. 



The mineral is readily soluble in hot nitric or hydrochloric acid. 



DATOLITB CRYSTALS FROM MERIDEN, CONNECTICUT. 



In a lot of minerals collected by the writer at Meriden, Connecticut, 

 in October, 1919, were a number of specimens of datolite. While the 



cr} stals show no new or rare forms 

 the habit is slightly different from 

 that of any previously figured Amer- 

 ican datolite, and since datolite from 

 this locality has not previoi.sly been 

 described, a short note on the occur- 

 rence is here presented. 



The quarry at Meriden is in the 

 Middle basalt sheet and is located 

 about 1 mile northwest of Meriden 

 station. The rock here is all more 

 or less amygdaloidal, and the amyg- 

 dules are filled with various sec- 

 ondary minerals, chiefly quartz, an- 

 hydrite, chalcedony, calcite, and 

 diabantite. The secondary minerals 

 also occur in narrow veins, some of 

 which persist for 50 or 75 feet, with 

 a width of 2 or more inches. The 

 datolite specimens were collected 

 FIG. 13.- CRYSTAL OF DATOLITE. A, ortho f^om such a vcln On the east side of 

 GRAPHIC PROJECTION. B, clinographic- ^^q dccpcst part of tlic quarry. The 



lEOJECTION. T , T, J. 1 ^ „4- 



datolite was present here as a coat- 

 ing of crystals directly deposited on the greatly altered trap, no 

 other mineral being associated with it. In another part of the quarry 

 a hollow amygdule in the trap, several inches in diameter, was lined 

 with small opaque white datolite crystals. 



^ 



B 



