158 



W. T. Schaller — Mineralogical Notes. 



5. Zinnwaldite from Alaska. 



The occurrence of zinnwaldite with cassiterite and topaz in 

 the York region, Alaska, has already been mentioned* and the 

 results of a quantitative analysis of this mica are here pre- 

 sented. The sample analyzed was probably fairly pure. 



Analysis 



Si0 2 46-80 



Al o 3 24-50 



F e ;o 3 -so 



FeO 6-35 



MnO 1-38 



CaO -24 



Na 2 1-73 



K 2 9-20 



Li 2 3-73 



H 2 -88 



F._ 8-63 



Ratio 



•775 

 •240 

 •003 

 •088 

 •019 

 •004 

 •033 

 •098 

 •124 

 •098 

 •454 



775 

 243 



111 



131 

 124 

 552 



-0 = 2F 



103-94 

 3-63 



100-31 



In the ratios, the soda and potash are taken together and the 

 small amount of water present is considered as hydroxyl and 

 added to the fluorine ratio. The empirical formula gives : 



Si 715 Al 486 F eill K 262 Li 248 F 662 2369 



The total oxygen is very slightly greater than three times the 

 silica, the ratio O : Si being 3*06 : 1. The mineral is therefore 

 considered as a metasilicate and the formula may be written 



(Si0 3 ) 776 (AlF 2 ) 276 K 262 Li 248 Fe in (A10) 44 Al )66 

 or 



(SiO 3 ) 12 (AlF 2 )' 4 . 27 K' 4 . 06 Li' 3 . 84 Fe" 1 . 72 (AlO)'. es Al'" 2 . 57 



The above formula shows that the analysis may well be 

 interpreted as a metasilicate. 



6. Forms of Pisanite — a Correction. 



In a paper on "Minerals from Leona Heights, Alameda Co., 



California,"f the writer described a number of new crystal 



forms for pisanite (Fe,Cu) S0 4 .7H 2 0. One of these, g= f§05| 



has to be withdrawn as its determination is based on an error. 



The face measured and described as { 205} is the base J001}. 



meas.{205}, <£ = 90° 03' p = 15° 00' 



calcfOOl}, <£ = 90 00 p=l5 11 



*Bull. 262 U. S. Geol. Survey, 129, 1905. 

 fBull. Dept. Geol. Univ. Col., iii, 191-217, 1903. 



