ox THE NATURE OF LOUISITE WALKER 



37 



The apophyllite was analysed by E. W. Todd with the 

 following result: 





% 



Molccu. jApophyl- 

 ratio i lite 



Bal. 



SiO^ 



53.64 



.12 



.18 



24.19 



.64 



4.42 



16.61 



.48 



(- .20) 



.893 

 .001 

 .001 

 .432 

 .010 

 .047 

 .923 

 .026 



864 



432 

 007 

 047 

 905 

 026 



029 

 001 

 001 



003 



018 



ALO, 



FeA 



CaO 



Na^O 



K^O 



H,0 



F 



Less oxygen equivalent 



100.08 



The molecular ratios of the different constituents are in- 

 dicated in the second column. In the third the constituents 

 which go to form the apophyllite, using the formula of Ram- 

 melsberg, 4CaO, 8SiO.. 8H3O' K(F.OH), are indicated. In the 

 last column the balance is very small, consisting of 1.74% SiO,, 

 .12 AI.O3, .18 Fe.Oj, .18 NaA and .32 H,0. Chemically con- 

 sidered, the lighter portion is very nearly pur^ apohyllite with 

 a little quartz and very slight mixture probably of some zeolite. 



The optical properties of the two minerals which make up 

 the aggregate known as louisite, were examined by ihe immer- 

 sion method and found to possess indices of refraction in accord 

 with the suggestion that the individual minerals are quartz 

 and apophyllite. 



I wish to acknowledge the kindness of Mr. Piers in permit- 

 ting me to examine the only known specimen of louisite. 



