ART. 22. 



A NEW LOCALITY FOR VELARDENITE — SHANNON. 



The analysis of the California material gives the following ratios; 

 Ratios of Veliirdenite from California. 



The composition of the m.aterial is thus capable of expression by 

 the formula 14Ca0.2Mg0.5Al203.9Si02. The velardena material 

 was interpreted by Schaller- as an isomorphous mixture of akerman- 

 ite, for which he adopted the formula 4Mg0.8Ca0.9Si02, and velar- 

 denite to which he assigned the formula 2CaO.Al2O3.SiO2. Taking 

 the present mineral as of similar constitution and using the magnesia 

 as an index to the akermanite present it gives: 



28 CaO. 4MgO. 10 AUO,. ISSiO^ 

 minus 8 CaO 4MgO. GSiOj Skerraanite 



leaves 20 CaO. 10 AUO,. 9S0, 



Taking for the formula for akermanite the 2CaO.MgO.2SiO.. found 

 by Ferguson and Merwin ^ the following results are obtained : 



14 CaO. 2MgO. 5A1,03. 9SiO. 

 minus 4 CaO. 2MgO. 4Si02 aljermanite X 2. 



leaves 10 CaO. 5AI2O3. SSiO... 



01- 2 CaO.AloOs.SiOsXS velardenite. 



It thus appears that the California mineral consists of velardenite 

 and akermanite in the ratio of 5 parts of the former to 2 of the latter 

 or of 71.6 per cent b}^ weight of velardeiiite and 28.4 per cent of 

 akermanite. Schaller calculated that the Mexican material con- 

 tained 80 per cent of velardenite and 20 per cent of akermanite. 



The artificial compound 2CaO.Al2O3.SiO2 was first prepared artifi- 

 cially by Weyberg and later by Shepherd and Eankin. Schaller, in 

 his theory of the melilite group,* showed that all of the chemical 

 peculiarities of the various members of the group could be explained 

 by interpreting the minerals as isomorphous mixtures of four end 

 members, namely, sarcolite (3CaO.Al203.3Si02), a theoretical soda 

 sarcolite (3Na26.Al203.3Si02), velardenite (2CaO.Al2O3.SiO2), and 

 akermanite (4Mg0.8Ca0.9Si02). The end member velardenite was 

 found to occur in excess in material called gehlenite from several 

 localities, but since the name gehlenite had obviously been given to 

 an intermediate mixture of two or more end members it was recom- 

 mended that this name be discarded. This series of minerals has 



2 Schaller, W. T., Bull. U. S. Geol. Survey No. 610, p. 106, 1916. 



" Ferguson, J. B., and Merwin, H. E., Proc. Nat. Acad. Sci., vol. 5, p. 18, 1019. 



* Schaller, W. T., TJ. S. Geol. Surv. Bull. 610, pp. 106-129, 1916. 



