A REVIEW OF THE AMORPHOUS MINERALS 535 



Larsen). The other minerals mentioned above (cyrtolite, etc.) are 

 probably synonyms of malacon. 



Halloysite. H^AUSiiOgCHaO)^ (myeline, indianaite, clayite, bole 

 in part, kaolin in part). — It is generally recognized that some 

 of the clays consist in whole or in part of amorphous aluminum 

 silicates. Mellor 1 has proposed the name clayite for the amorphous 

 constituent, but fortunately halloysite has priority. 



Halloysite may be regarded as the amorphous equivalent of 

 crystalline kaolinite, for it has the formula H 4 A1 2 S^Og-f^C^LX).) In 

 LeChatelier's experiments on halloysite the water given off below 

 250 C. varied within wide limits, while the water given off above 

 this temperature was fairly constant and corresponded to that of 

 kaolinite. 



Myeline is an indurated clay from Rochlitz, Saxony, which is 

 almost identical with kaolinite in chemical composition. I have 

 examined a specimen from the type locality and find it to be 

 essentially amorphous (there are patches of micro-crystalline 

 material) with an index of refraction of i.556="=o.ooi. Gagel 2 has 

 described a non-crystalline myeline-like substance which occurs as 

 an alteration product of trachydolerite at Canical, Madeira. 



I have examined indianaite from St. Lawrence County, Indiana, 

 which the published analyses show is a very pure halloysite, 

 and find it to be an amorphous mineral with an index of 

 refraction of 1. 538=!= 0.002, which is less than that of kaolinite 

 (n= i. 567- 1. 561). 



A clay from Morton, Minnesota, with imperfect pisolitic struc- 

 ture consists largely of an amorphous substance with an index of 

 refraction of 1 . 557=^=0. 003, and hence may be referred to halloysite. 

 This clay also contains some hydrargillite. 



I have examined "kaolin" from Broken Hill, New South Wales, 

 and find it to be amorphous with n= 1. 548=^0. 002. This must 

 be halloysite. 



The " isotropic kaolinite-like mineral" described by Larsen and 

 Wells 3 from Wagon Wheel Gap, Colorado, has an index of refraction 



1 Trans. Eng. Cer. Soc, VIII (1908). 



2 Central./. Min., Geol., u. Pal., 1910, p. 225. 



3 Proc. Nat. Acad. Sci., II (1916), 364. 



