Hidden and Pratt — Rhodolite, a new variety of garnet. 295 



and sperrylite in minute quantities, and also several as yet 

 unidentified species. It is our intention to publish a descrip- 

 tion of some of these accompanying minerals in the near 

 future. 



As yet no crystals of the new garnet have been found, all 

 the material occurring as rolled pebbles, fragmentary masses or 

 as highly etched (naturally corroded) pieces. The predominant 

 color is a pale rosy tint inclining to purple, and some carefully 

 selected pieces of this character, which showed no inclusions 

 under the magnifying glass, were used for the chemical analysis. 



In the analyses, silica and the bases were determined by the 

 well known methods. Ferrous and ferric oxides were deter- 

 mined by the method described by one of us.* The results of 

 the analyses are given below together with the specific gravity 

 which was determined upon two separate samples. 



Specific gravity = 3*837 — 3-838. 



Ratio. 



•237 = 1-02 

 •669 = 2-89 



100-32 



The ratio of E"0 : R'" 2 3 : Si0 2 is nearly 3:1:3, which 

 would give the general formula ZR!'Q . R //7 2 3 . 3Si0 2 or 

 E, // 3 K /// 2 (Si0 4 ) 3 which classifies this mineral as one of the 

 garnets. The ratio of MgO to FeO (-437: '216) is almost 

 exactly 2 : 1, which would indicate that the mineral is composed 

 of two molecules of a magnesium-aluminum garnet (pyrope) 

 and one molecule of a ferrous iron-aluminum garnet (alman- 

 dite). The theoretical composition calculated for this ratio is 

 given below, together with the analysis after substituting for 

 Fe 2 3 its equivalent of A1 2 3 and for CaO its equivalent of 

 MgO and then recalculating to 100 per cent : 



Analysis Theory for 



recalculated. 2Mg 3 Al 2 (Si0 4 )3 . Fe 3 Al 2 (Si0 4 )3. 



Si0 2 41-76 41-48 



A1 2 3 -._ 24-41 23-50 



FeO 15-62 16-59 



MgO 18-21 18-43 



100-00 100-00 



* J. H. Pratt in this Journal, vol. xlviii, 1894, p. 149. 





I. 



II. 



III. 



Average. 





Si0 2 .... 



41-54 



41-65 





41-59 



•693 



A1 2 3 __. 





23-26 



23-10 



23-13 



•226 



Fe 2 3 __ 



1-88 



1-92 





1-90 



•011 



FeO ... 



15-48 



15-63 





15-55 



•216 



MgO... 





16-90 



17-48 



17-23 



•437 



CaO ... 



1-02 



•86 





•92 



•016 



