A. F. Rogers — Lawsonite from California. 



109 



extinction and the elongation is parallel to the fast ray. From 

 these tests it is evident that the crystals are prismatic in the 

 direction of the «-axis. A rough water determination gave 

 12*97 per cent. 



Region east of Mt. Hamilton. 



Specimens of vein material in a metamorphic rock collected 

 in the region east of Mt. Hamilton show small 3 mm acicular 

 crystals of lawsonite in a matrix of quartz. In thin sections 

 the lawsonite appears as in fig. 8. Cross-sections are irregular 

 or rhombic with the fast ray parallel to the long diagonal 



Fig. 5. 



Fig. 6. 



Fig. 7. 



Fig. 5. Lawsonite from Mt. Hamilton region. 



Fig. 6. Lawsonite from Alameda County. 



Fig. 7. Lawsonite from Colorado Creek, Santa Clara County. 



while longitudinal sections are elongate, rectangular with more 

 or less frayed ends and are in part parallel to the slow ray, in 

 part parallel to the fast ray. Hence the crystals are prismatic 

 in the direction of the a-axis with habit something like fig. 1. 

 The optical orientation is a = a, b = /3, c = y. The double 

 refraction (ny—n a ), determining the thickness of the slide 

 by taking the highest interference color of the quartz, is '022, 



which is 

 Ransome. 



a little higher than the value (*019) obtained by 



Southeastern Alameda County. 



Bowlders of a massive lawsonite-chlorite rock were found in 

 the extreme southeastern corner of the Tesla topographic sheet 

 of the United States Geological Survey. The lawsonite occurs 

 in tabular crystals of 5 ,nra diameter and -J- mm thickness. The 

 forms are cjOOl}, m\110\, and b{010\. 



The habit is pseudo-hexagonal due to equal development of 

 m and 5, though the angle (110 : 110) is 67°. The optical 

 orientation is a — a, b = /3, o = y. The rock contains lawsonite 

 and chlorite with subordinate titanite in minute granular 

 crystals. 



Lawsonite from Colorado Creek, Santa Clara County. 



This locality for lawsonite is on Colorado Creek just south 

 of the divide between the Arroyo Mocho and Colorado Creek 

 in the northeastern part of the Mt. Hamilton topographic 



