6 PROCEEDINGS OF THE NATIONAL MUSEUM vol.70 



oxide as minor constituents. The ratio of manganese to zinc is about 

 3:2. The theoretical composition for these ratios is given in Table 1. 

 The formula may also be written RsAsjOg. 7R (0H)2. It is therefore 

 a hydroxyarsenate of manganese and zinc in which the ratio of hydrox- 

 ide to the arsenate is remarkably high. 



RELATIONSHIPS 



In respect to the ratio of the arsenate to the hydroxide this mineral 

 is quite exceptional. No other arsenate or phosphate approaches 

 this ratio. Chondrarsenite, to which the formula Mn3As208. 3Mn 

 (0H)2 had been assigned, is now known to be sarkinite, Mn3As208. 

 Mn (0H)2. The doubtful mineral xantharsenite to which the formula 

 5MnO.As2O5.5H2O has been assigned approaches nearest to chloro- 

 phoenicite. A specimen of this mineral from the collection of Colonel 

 Washington A. Roebling has the following optical properties: Yellow 

 structureless veins, biaxial positive, 2V medium, a= 1.705, 18= 1.710, 

 7=1.720. Neither the chondrarsenite nor the xantharsenite have 

 been found in crystals. They show considerably more arsenic and 

 less bases and differ appreciably in certain optical features. Chloro- 

 phoenicite is apparently quite distinct from either of these and is not 

 related closely to any known mineral. 



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