Vol. 5] 



Louderback. — Benitoite. 



357 



Chemical Characters. 



It is practically insoluble in hydrochloric acid and may there- 

 fore be chemically separated from the natrolite matrix as is the 

 case with the benitoite. 



Professor Blasdale's quantitative analysis is here given, and 

 for comparison, two made on the Greenland neptunite, the first 

 by Flink, the second by Sjostrom. 13 



Neptnnite (Greenland) California Mineral Molecular ratios for 





I 



11 



III 



III 



Si0 a 



51.53 



51.93 



53.44 



.820 



Ti0 2 



18.13 



17.45 



17.18 



.213 



FeO 



10.91 



10.23 



11.23 i 





MnO 



4.97 



5.32 



1.78 



.230 



CaO 





0.71 



0.25 



MgO 



0.49 





1.82 j 





K 2 



4.88 



5.71 



5.39 1 



.204 



Na,0 



9.26 



9.63 



9.14 J 







100.17 



100.98 



100.23 





He says "The results show a substantial agreement in the 

 composition of the mineral from the two localities, the most 

 marked differences apparently resulting from the substitution of 

 magnesium and iron for some of the manganese in the Greenland 

 specimens. Sjostrom represents the composition of the mineral 

 by the formula ROR 2 O.Ti0 2 .4Si0 2 and the same form can be 

 applied with equal degree of success to the new analysis." 



NATROLITE. 



Natrolite is the gangue in which the benitoite and neptunite 

 occur, and it is also found in veinlets without associates. 



Fracture of the solid vein-stone shows a mass of xenomorphic 

 crystals exhibiting a good cleavage that yields more or less curved 

 surfaces. The general texture is granular but with common 

 development of radiate forms quite different from the usual 

 radiate arrangement of natrolite and not showing such distinct 

 straight-line boundaries to the components. 



Where open spaces occur in the veins allowing the formation 

 of crystal faces, peculiar aggregates are found entirely unlike the 



isGeol. Foren. Forh., 15 (1893), p. 393. 



