CONTRIBUTIONS FROM THE HARVARD MINERALOGICAL 



MUSEUM. 



VIII. — ON HARDYSTONITE AND A ZINC SCHEFFERITE 



FROM FRANKLIN FURNACE, NEW JERSEY. 



By John E. Wolff. 



WITH A NOTE ON THE OPTICAL CONSTANTS 



OF THE SCHEFFERITE. 



By Dr G Melczer. 



Received June 21, 1900. 



a. Hardystonite. 



The new mineral hardystonite described in these Proceedings * was 

 found in small grains in a mass of zinc ore and isolated by handpicking 

 and the use of heavy solutions, while the (tetragonal) crystal system was 

 determined by the study of thin sections of the grains. When visiting 

 the mine in September, 1899, I received from the mine officials pieces 

 from a large mass of neai-ly pure Hardystonite, several inches in diame- 

 ter, which had been found in the same workings as the original mineral. 

 The material is grayish-white in color, often streaked or clouded by faint 

 pinkish tints, and breaks into angular fragments owing to the presence of 

 several cleavages ; the lustre is glassy on the more perfect cleavages, 

 elsewhere faintly resinous. It was easy to select material for thin sec- 

 tions oriented parallel to the basal and prismatic cleavages and for pol- 

 ished plates parallel to the base, from which the indices of refraction 

 were determined and the original statement confirmed; namely, that the 

 mineral is tetragonal and optically negative, has a basal cleavage and 

 primatic cleavages parallel to the prisms of the first and second orders — 

 iu addition, traces of a pyramidal cleavage were observed. 



By means of the Abbe total rellectometer the indices of refraction 

 were determined on a plate parallel to the base as follows : 



* Tliese Proceedings, XXXIV. 479, 1899. 



VOL. XXXVI. — 8 



