330 S. L. Pen field — Crystallization of Herderite. 



ral is herderite and that it contains practically no fluorine, agree- 

 ing in this latter respect with a variety described by Professor 

 Wells and the author- from Hebron, Me. The analyses of the 

 minerals from both localities are as follows : 







Hebron 









after deducting 









527 per cent 



Theory for 





Paris. 



of impurities. 



Ca[Be(OH)]PO. 



Sp. gr 



2-952 



2-975 





P 2 o 5 



. 44-05 



43-08 



44-10 



BeO 



16-18 



16-18 



15-53 



CaO 



34-04 



[34-35] 



34-78 



H„0 



5-85 



6-15 



5-59 



F" 







•42 





Insoluble 



0-44 











100-51 100-18 100-00 



The analyses indicate a well defined type of herderite which 

 may well be called hydro-herderite in distinction from the 

 variety containing fluorine. Of the two types the former, 

 Ca[Be(OH)]P0 4 , occurs quite pure, as shown by the above 

 analyses, and it may readily be told by its peculiar behavior 

 when heated in a closed tube. We have as yet no proof of 

 the existence of a pure fluor-herderite Ca[BeFjP0 4 . Mackin- 

 toshf advanced such a formula for the mineral from Stone- 

 ham, Me., but he did not make a test for water or a direct 

 determination of fluorine, the latter being calculated, as he 

 states, from the excess of lime. The author in connection 

 with Mr. D. ~N. Harper:}: proved that the Stoneham herderite 

 contained both hydroxyl and fluorine in the proportion of 

 about 3:2 and proposed the formula Ca[Be(OH .F)]P0 4 , 

 where fluorine and hydroxyl are regarded as isomorphous. 

 This last type, which may be designated as hydro-fluor-her- 

 derite, may be readily distinguished by its behavior in a closed 

 tube, as, when heated intensely, acid water is driven off, etch- 

 ing the glass and yielding a deposit of silica. From the quan- 

 tity of hydrofluoric acid that is liberated it has been assumed 

 that the fluorine and hydroxyl are in combination with beryl- 

 lium and not with the more basic calcium. 



The most interesting feature of the herderite from this new 

 locality is, however, its monoclinic crystallisation. The- dis- 

 covery of this has lead to the examination of the mineral from 

 other localities and it has been found, as will be shown in the 

 course of this article, that herderite is always monoclinic and 

 not orthorhombic. 



*This Journal, III, xliv, p. 114. 1892. 

 fThis Journal, III, xxvii. p. 137, 1884. 

 \ This Journal, III, xxxii, p. 107, 1886. 



