Ransomk. I 



Lawsonite. 



307 



age previously described. 1 11 fact, the bands of color and this cleav- 

 age stand in very close relation, the latter being far more readily seen 

 in such crystals or portions of crystals as show the blue pleochroisni. 

 Between crossed nicols, the pleochroic and non-pleochroic portions of 

 the crystal are optically continuous, but show a perceptible difference 

 in double refraction. The fact that the pleochroic zones and bands 

 are usually found on the peripheries of the larger crystals, suggested 

 that the pleochroisni might possibly be a secondarily derived prop- 

 erty, but this is now thought doubtful. 



In thin sections of the schist, the bright polarization colors 

 and high relief of the mineral are decidedly striking. Pleochroisni 

 can very rarely be detected in slides of the ordinary thickness. 



CHEMICAL COMPOSITION. 



Two chemical analyses of lawsonite have been made, and are 

 given below in tabular form, with their molecular ratios, the derived 

 formula, and the theoretical composition. 



TABLE SHOWING ANALYSES OF LAWSONITE, AND DERIVATION 

 OF ITS CHEMICAL FORMULA. 





1. 



Molecular 

 Ratios. 



Reduced 

 Ratios. 



11 



Molecular 

 Ratios. 



Reduced 

 Ratios. 



Mean 

 of 



I and II. 



Molecular 

 Ratios. 



Reduced 

 Ratios. 



Theoretical 

 composition 



deduced 

 from 



formula. 



SiO, 



38.10 



■635 



I.92 



37-32 



.622 



i-95 



37-71 



.628 



i-93 



38.09 



A1A, 



28.88 























•8 5 



| .2S8 



.87 



| 35- 14 



•341 



1.07 



32.43 



•314 



•93 



32.69 



CaO 



18 26 







17-83 



.318 



1. 00 



18.15 



•324 



1. 00 



I7.77 



MgO 



•23 



|-330 



I. OO 

















Na,0 



.65 









































H.O 



1 1.42 



• 634 



I.92 



11.21 



1 



.622 



i-95 



II. 31 



.625 



1.92 



H-45 



Totals 98.39 







101.50 







QQ.6O 







100.00 



Formula : H 4 CaAl,Si 2 



