116 



C. H. Warren — Mineralogical Notes. 



Art. XL — Mineralogical Notes; by C. II. Warren. 



1 . On the occurrence of Melanotelcite at Hillsboro, Neio Mexico, and 

 on the Chemical Composition of Melanotelcite and Kentrolite. 



The rare mineral melanotekite, a basic silicate of ferric iron 

 and lead, was first described in 1880 from Lftngban, Sweden, 

 by G. Lindstrom* It was there found as massive material, but 

 crystals of it from Pajsberg, Sweden, have since been described 

 by Nordenskioldf, who has shown that they are orthorhombic, 

 and similar to kentrolite, a corresponding basic silicate of 

 manganese and lead. The material to be described in the 

 present paper was recently sent to the Mineralogical Laboratory 

 of the Sheffield Scientific School for identification by Mr. W. 

 M. Foote, of Philadelphia, Pa., and later an excellent specimen 

 was received from Mr. J. H. Porter of Denver, Col. Both 

 parties had obtained their material from Mr. Geo. E. Robin of 

 Hillsboro, New Mexico, who had collected it at the Hex and 

 Smuggler mines at Hillsboro, where it is associated with cerus- 

 site and a brown, jasper-like, material. The material has a 

 dark brown to almost black color, and gives an ochre -yellow 

 streak, similar to that of limonite or gothite. The specimens 

 consist for the most part of a rather compact mass of crystals, 

 showing distinct forms in numerous cavities. The largest 

 crystals measured about 0"5 mm in length, and considerably less 



in diameter, and showed the sim- 

 ple combinations represented by 

 Figs. 1 and 2. They were always 

 attached, and frequently in such 

 a manner that both ends of the 

 crystal could be observed. 



The forms which have been 

 observed are as follows : 



b, 010 



m, 110 



k, 150 



Usually m and b are the only 

 faces in the prismatic zone, but the prism n was seen on a 

 number of crystals, while k was observed only once. The 

 crystals were always terminated by the pyramid o. Considerable 

 difficulty was experienced in selecting crystals from which 

 satisfactory measurements could be obtained, as the faces w r ere 

 not only small, but generally vicinal, thus rendering the refl.ec- 



* Ofv. Ak. Stock., xxxv, No. 6, 53, 1880. 

 f Geol. Foren. Forh., xvi, 151, 1894. 



