Brush and Dana — Min< I'd/ Locality at Branchvtile. 207 



ite, tin' triphylite group receives an important addition, and 



we now have : 



Triphylite, LiFePOi } Connected by many intermediate 

 Lithiophilite, LiMnP0 4 ) compounds. Li(Pe, Mn)PO«. 

 Nfttrophilite, NaMnPJ »,. 



These three species are, as is to be expected, closely isomor- 



phous. To them is also related in composition and in some 

 degree in form the new sodium-beryllium phosphate, beryllo- 

 nite, NaBeP0 4 , which was described by one of us a year and a 

 half ago.* 



The relation of natrophilite in origin to the common lithio- 

 philite is an interesting question. In view of the extensive 

 changes that, as we have shown, have taken place in the spo- 

 dumene, by which the lithium has been removed and its place 

 taken more or less fully by sodium, or sodium and potassium, 

 it is natural to suggest that a similar change has resulted in 

 forming the NaMnPO, out of LiMnP0 4 , and this we regard as 

 very probable. Its limited method of occurrence suggests the 

 >ame thing, although it must be remarked at the same time that 

 it seems to pa>s into hureaulite as readily as the litliiophilite. 

 If in fact formed from litliiophilite, the change probably took 

 place before the formation of most of the other phosphates. 



Hureaulite. 



Perhaps the most interesting of recent developments at 

 Branchville is the discovery of the rare mineral hureaulite. 

 Thus far our knowledge of hureaulite has been limited to the 

 account of crystals from Limoges by Dufrenoyf and the later 

 and more thorough description by Damour and DesCloizeaux.^ 

 In addition we have only the single remark by Websky that it 

 probably occurs at Michelsdorf, Silesia, with sarcopside. 



The crystals described by DesCloizeaux belong to three 

 varieties showing two distinct types of form, though having the 

 same composition, as shown by Damour. These varieties are 

 respectively violet-rose, brownish orange and pale rose pink in 

 color. Their crystal lographic relation to each other is anoma- 

 lous, in fact, it would be difficult to find another case equally 

 so. The crystals of the two types have the fundamental prism 

 in common, but otherwise no plane of the one occurs on the 

 other, and what is more remarkable, the symbols assigned to a 

 number of the planes of the second type are complex in the 

 extreme. The axial ratio calculated from DesCloizeaux's fun- 

 damental measurements is 



d:b:'c= 1-6977: 1 : 0-8887 ; p = 89° 27'. 



The planes observed on crystals of the two types are as follows : 



* This Journal, xxxvi, 290, Oct., 1888; xxxvii, 28. Jan , 1889. 



f Ann. Chim. Phys., xli, 338, 1829. \ Ibid, III, liii, 293, 1858. 



