No. 2118. ALLOPHANITE, FUCHSITE, AND TRIPHYLITE— WHERRY. 465 



and HjO 1.31, the first two were averaged in the ratio of 3:2, giving 

 1.592 as the index of anhydrous allophanite, and this was then aver- 

 aged with the figure for HjO in the several proportions listed. The 

 essential agreement between the observed and calculated values indi- 

 cates clearly the additive character of the indices; that is, the index 

 of any combination is the average of the indices of its components. 



Qualitative tests: Decomposed by HCl, yielding granular siUca; 

 gives reactions for Al, Ca, and traces of Mg and Fe. Before the 

 blowpipe: Gives reactions for Al, Si, and OH. 



Analysis, made on microscopically homogeneous, amorphous 

 material : 



Ratios. 



AI2O3 33. 78 0. 331 1. 



FeaOa 1.08 .007 



SiOj 21.70 .360 1.1 



CaO 2.04 .036 



MgO 0.45 .011 



H2O below 100° 4.86 .270 



H2O above 100° 35. 82 1. 990 6. 



Total 99. 73 



The tendency of the coUoidal alumina and silica to unite in the 

 definite ratio 1:1 here shown is a good example of Cornu's law of 

 homoisochemism,but the additive character of the indices of refraction 

 of the constituents indicates that no complete chemical combination 

 has occurred between them. 



TWO NEW OCCURRENCES OF FUCHSITE. 



The name fuchsite, proposed by Schafhautl in 1842, is used to refer 

 to the isomorphous series of which H^K (AlSi04)3 and HjK (CrSi04)3 

 are the end members, the first being usually present in excess over the 

 second. 



Fuchsite from Chester County, Pennsylvania. — On Young's farm, 2 

 miles west of Harmony Hill, on the north side of the road to Romans- 

 ville, West Bradford Township, a deposit of a bright-green mineral 

 has long been known to local mineralogists, and specimens from it 

 included in collections, usually under the name epidote, but it was 

 identified as fuchsite in 1907.* The rock consists of a fine-grained 

 dolomite, contaming considerable granular quartz, and in certain 

 zones and streaks abundant flakes of colorless to intense green mica.^ 

 Although occurring only as isolated ledges in the bank of a brook, sur- 

 rounded by soil containing fragments of mica schist and gneiss, and 

 showing no determinable relations with any known formation of the 

 region, it is probably the result of alteration of a dike of some basic 

 igneous rock, such as chromite-bearing serpentine. A somewhat 

 similar occurrence has been described in Montgomery County, Mary- 



1 Mineral Collector, vol. 14, 1908, p. 172. « Cat. No. 87610, U.S.N.M. 



81022 °—Proc.N.M. vol.49— 15 30 



