554 Wright — Three Contact Minerals. 



This analysis agrees closely with the formula Ca 3 Si0 4 .H a O,* 

 it being a little higher in silica and lower in lime, a condition 

 which is evidently due to a slight leaching of the lime. The 

 water of the analysis was determined by loss in weight, the 

 figure given being the average of two determinations, 9*34: 

 and 9'39. By absorption by calcium chloride plus the little 

 obtained at 110° the result was 918. The first figures, how- 

 ever, are more accurate. 



Hillebrandite occurs usually with few inclusions and even 

 magnetite is rare. Occasionally small grains of carbonate, 

 yellow garnet and wollastonite occur with it and also earthy 

 material of a secondary nature. Yeinlets of wollastonite 

 traversed several of the hand specimens and in each case the 

 direction of elongation of the wollastonite fibers was normal 

 to the vein walls. 



Experiments to produce hillebrandite synthetically have 

 thus far not proved successful. 



The above optical and chemical data show beyond question 

 that hillebrandite is a true chemical compound of unique 

 chemical composition. It is with great pleasure, therefore, 

 that the writer suggests the above name as a token of appre- 

 ciation of the fundamental researches of Dr. W. F. Hillebrand 

 of the IT. S. Geological Survey in mineralogical chemistry. 



Geophysical Laboratory. 



Carnegie Institution of Washington, 

 Washington, D. C. 

 June, 1908. 



* This formula may also be written CaSi0 3 .Ca(OH) 2 or simply H 2 0. 

 2CaO.Si0 2 . 



