50 TL L. Wells and S. L. Pen field — Gerhardtite, etc. 



Art. VIII. — Gerhardtite and Artificial Basic Cupric Nitrates, 

 by H. L. Wells and S. L. Penfield.* 



"We shall describe in the present article a natural, crystallized 

 basic cupric nitrate and a crystallized artificial salt of the same 

 chemical composition but of different crystalline form. We 

 also give an account of a re-investigation of two basic cupric 

 nitrates to which have been ascribed different compositions, but 

 which, as we shall show, have the same composition as the 

 basic nitrates described by us and by other investigators, whose 

 results will be briefly summarized. 



Gekhardtite, a new mineral. 



This mineral was first identified as a new species by Prof. 

 Geo. J. Brush, who found it among a lot of copper minerals 

 from the United Verde Copper Mines, Jerome, Arizona, which 

 were left at the Sheffield Scientific School by Mr. Gr. W. 

 Stewart, assayer, from that place. 



The single specimen in our possession consists of a small 

 piece of very pure massive cuprite, along a crack in which the 

 crystals of the nitrate occur, together with acicular crystals 

 of malachite. The crystals, 4— 6 mm in diameter, were few in 

 number and were almost wholly sacrificed to obtain mate- 

 rial for investigation. An attempt has been made to obtain 

 more of the material, but as yet no other specimens have 

 been received, although we are in hopes that more may be 

 found at the locality. From the abundance of crystals on the 

 specimen in our possession, it would seem that there must have 

 been a quantity of it found. It was probably regarded as 

 malachite by the miners. Another specimen contains crystals 

 of atacamite on the cuprite. 



The crystals, which were carefully separated from the cuprite, 

 were subjected first to crystallographic, then to chemical exam- 

 ination. About 0*8 of a gram was obtained almost perfectly 

 pure, the only impurity being a few acicular crystals of mala- 

 chite which sometimes penetrated the nitrate but were visible 

 only under the microscope. 



The hardness of the mineral is 2. Specific gravity 3'426. 

 Color dark green. Streak light green. Transparent. 



The crystals after being detached were only fragmentary. 

 All those suitable for measurement were reserved. They were 

 very fragile and had to be separated and handled with very great 

 care. The crystals are orthorhombic, having the habit shown 



* The chemical work is by the former, the crystallographic by the latter. 



