A. F. Rogers — Law sonite from California. 



107 



m thick, and in 



are about l cm in length, 4 nim in width, and 2 

 habit are prismatic in the direction of the &-axis. The forms 

 are d\0ll\, m\110\, and cjOOlf, as represented in figure 1. 

 This habit is so different from that of the Tiburon crystals that 

 it was not at first suspected to be lawsonite. There is distinct 

 cleavage parallel to m and to c. The optical orientation is 

 a = a, b = /3, c=7. 



Fig. 1. 



Fig. 2. 



Fig. 3. 



Fig. 1. Lawsonite from Arroyo Mocho, Alamedo County. 

 Fig. 2. Lawsonite from Calaveras Valley, Santa Clara County. 

 Fig. 3. Lawsonite from Calaveras Valley, Santa Clara County. 



An analysis of this lawsonite was made by Mr. H. L. Small 

 under the writer's direction. The results, which are the aver- 

 age of two, are given in column I. The lawsonite is pure 

 except for a little calcite, which is probably an alteration prod- 

 uct. Subtracting the carbon dioxide and an equivalent amount 

 of lime and recalculating to 100 per cent, we have the figures 

 of column II, while the theoretical percentages for H 4 CaAl 2 

 Si 2 O 10 are given in column III. 



Analysis of Law sonite from Arroyo Mocho. 



I II III 



Sio 2 _ 38-10 38*70 38-34 



A1 2 3 _ _. 32-21 32-60 32'44 



CaO 17-74 17*70 17*80 



MnO nil 



MgO nil 



Ti0 2 _ nil 



CO, 1*12* 



H 2 0... 10-85* ll'OO 1L42 



Total... 100*02 100-00 100-00 



* The water was determined by the Penfield tube method, while combined 

 water and carbon dioxide were determined by loss on ignition. 



