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PEOCEEDIISrGS OF THE NATIONAL MUSEUM 



VOL. 71 



of them have the same habit, the dodecahedron d{110) modified by- 

 narrow faces of the hexoctadedron s(321). Rarely the dodecahedron 

 alone is present, and in a few specimens the hexoctahedron forms 

 the dominant faces, reducing the faces of the dodecahedron to minute 

 size. 



]Minerals associated with this garnet in the 30 crj^stallized speci- 

 mens included in the collection include diopside, vesuvianite, epidote, 

 l^yrite, and the zeolites, chabazite, stilbite, heulandite, and scolecite. 

 While the diopside is probably contemporaneous with the garnet in 

 part, all the others rest upon the garnet crystals or occupy the 

 interstices between them and seem later. 



This buff garnet was analyzed by Eakins, but the exact specimen 

 used for the analysis is not indicated, 24 having the same number. 

 The analysis is given below\ 



Analysis, of buff garnet 

 [L. G. Eakins, analyst] 



The ratios obtained from this analysis indicate very exactly the 

 garnet formula, 3R"0. R" ^Oa. 3Si02, and the absence of ferrous 

 iron, magnesia, and manganese indicate that it is a simple two-com- 

 ponent isomorphous mixture of the lime-alumina garnet gros- 

 sularite, CagAljSisOia? and the lime-ferric iron garnet andradite, 

 CasFe'^ 'oSisOii- The above garnet analysis indicates these two 

 compounds to be present in the proportions of 86 per cent of gros- 

 sularite to 14 per cent of andradite. The specific gravity of the 

 analyzed sample was determined by Eakins to be 3.629 at 23° C. 

 The calculated specific gravity for a garnet of this composition from 

 Ford's data for the end members is 3. .561, the difference 0.068 prob- 

 ably indicating an error in the determination. 



Unfortunately, the refractive index of the analyzed sample was 

 not determined. The calculated refractive index for the above com- 



