S. L. Penfield — Cookeite from Maine. 



395 



Cookeite is associated with quartz, lepidolite and tourmaline 

 (especially the variety rubellite) and apparently has resulted 

 from the alteration of the latter, as suggested by Professor 

 Brush. One of the best and most interesting specimens of the 

 mineral in the Brush collection is a deposit of the mineral on 

 a large tourmaline crystal. This latter has a triangular pris- 

 matic habit, terminated by a basal plane and is over 4 cm in 

 diameter. As a subsequent process the tourmaline has been 

 mostly removed, leaving a cellular interior, containing cookeite, 

 a few quartz crystals and remnants of the original tourmaline, 

 etched out into slender prisms and spicules reminding one of 

 the etched beryls (aquamarines) from Mt. Antero, Colorado.* 

 The cookeite here is plainly a secondary mineral and in this 

 respect, as well as in its crystalline habit, mode of twinning 

 and optical properties it is related to the chlorites. It is also 

 like some varieties of vermiculite in its pyrognostic properties. 

 When heated before the blowpipe it exfoliates prodigiously, 

 giving at the same time a lithia color to the flame. 



The material for analysis was carefully selected from a speci- 

 men from Paris where the cookeite was associated with quartz 

 and tourmaline, thereby avoiding any contamination with 

 lepidolite. The results of the analysis are given below to- 

 gether with the original analysis of Mr. Collier. 









Author. 







Collier. 





Specific 



gravity 



■ 2-675 







2-70 





I. 



II. 



Mean. 



Eatio. 





Mean. 



Si0 2 



34-00 





34-00 



•567 



4-00 



34-93 



A1 2 3 



45-13 



44-98 



45-06 



•442 



3 11 



44-91 



Fe 2 3 



0-45 





0-45 









CaO 



0-04 





0-04 









K 2 



0-11 



0-16 



0-14 



•001 ) 





2-57 



Na 2 



0-20 



0-17 



0-19 



•003 V -138 



0-97 





Li 2 



4-14 



3-89 



4-02 



•134 ) 





2-82 



H 2 



14-85 



15-06 



14-96 



:^h 43 



5-94 



13-79 



F 



0-46 

 ivalent to the F 



0-46 -=-38 



SiF 4 0-47 



equ 



99-32 



99-49 









19 









99-13 



The ratio in the author's analysis corresponds closely to 

 Si0 2 : A1 2 3 : Li 2 : H 2 = 4:3:1:6 giving the formula 

 H 12 Li 2 Al 6 Si 4 24 , or simplified to that of a basic metasilicate, 



Am. Jour. Sci. 

 28 



* This Journal, III, xl, p. 488, 1890. 

 -Third Series, Vol. XLV, No. 269.— Mat, 1893. 



