534 AUSTIN F. ROGERS 



and often contains the sulfate radical. An artificial colloidal basic 

 ferric arsenate has been described by Holmes and Rundfusz. 1 



I have examined specimens of pitticite from two localities, one 

 on the west side of the South Merced River in Mariposa County, 

 California, and the other at Sioux City, Iowa. At the first locality 

 it is an oxidation product of arsenopyrite and at the second it 

 occurs with limonite and aragonite. 



Pitchblende \J0 2 ,\J0 3 ,(K 2 0) x (Uraninite in part, nasturan).— 

 The colloform or massive pitchblende seems to be the amorphous 

 equivalent of isometric uraninite. Its water content is higher and 

 its nitrogen and rare earth content lower than that of uraninite. 

 It may also be distinguished by its lower specific gravity (6.5 to 8; 

 uraninite is 9 or above). 



Uraninite occurs in pegmatites while pitchblende occurs in 

 metalliferous veins with sulfids. 



(Maskelynite) ? — -Maskelynite was first described by Tschermak 

 from the Shergotty (India) meteorite. It is optically isotropic and 

 in composition is very close to a plagioclase with equal molecular 

 percentages of albite and anorthite. As the index of refraction 

 is almost exactly the same as that of an artificial glass 2 of the compo- 

 sition AbjAnr, it is probably the amorphous equivalent of plagioclase 

 (not necessarily a fused plagioclase) and not an isometric mineral. 



Maskelynite is on the same footing as lechatelierite. They are 

 the only glasses which have been regarded as minerals within recent 

 years. They may be disposed of by considering them mineraloids 

 rather than as definite minerals. 



Malacon. ZrSi0 4 (H 2 0) a; ? (cyrtolite, auerbachite, oerstedite, 

 ostranite). — Malacon is the name given to a mineral from Hittero, 

 Norway, which has the form of zircon, but is softer and contains 

 water. It is undoubtedly an alteration product and in all probabil- 

 ity the amorphous equivalent of zircon. It deserves recognition 

 as a distinct mineral, and Lacroix so regards it. 



Malacon may be distinguished from zircon, not only by its 

 isotropic character and water content, but also by its inferior hard- 

 ness and specific gravity and its lower index refraction (n= 1.826 



1 Jour. Am. Chem. Soc, XXXVIII (October, 1916), 1970. 



2 Larsen, Am. Jour. Sci. (4), XXVIII (1909), 267. 



