H. L. Wells and 8. L. Penfield — Gerhardtite, etc. 53 



We propose for this beautiful and unique mineral, the only 

 insoluble nitrate yet found in nature, the name Gerhardtite 

 from the chemist who first determined the true composition of 

 the same compound* made artificially. 



Crystallized Artificial Basic Cupric Nitrate. 



This is made by heating a solution of the normal nitrate with 

 metallic copper in a sealed tube to about 150° for a day or 

 more. The crystals form just above the surface of the liquid 

 on the walls of the tube. When the contents of the tube are 

 agitated the crystals fall to the bottom of the liquid where they 

 remain undissolved while another crop is being formed. Cu- 

 pric nitrite is apparently one of the products of the reaction ; 

 consequently the method is essentially a modification of that 

 used by Yogel and Keischauerj- in making the same compound 

 in light, iridescent scales. 



The crystals are of a beautiful dark green color, exactly the 

 same as that of the mineral, with a very brilliant luster. Spe- 

 cific gravity 3*378. The largest which we succeeded in making 

 were 7 or 8 mm in length. Their form 2 



is monoclinic as is shown both by ^- 



measurement and by their optical prop- ^■-/S.'".". 

 erties. Their habit is tabular, length- A ..-■■• c f 

 ened out in the direction of the b axis, 



fig. 2. The axial ratio was determined from the following 

 measurements : 



c^a 001/, 100 = 85° 27' 

 c~d 001/, 101 = 48° 25£' 

 e~e OU/,011 = 82° 41' 



giving a: 6: c = -9190: 1: 1-1402; (3 = 85° 27' 



The observed forms are 



a, 100, i-l d, 101, l-l 



c, 001, e, 011, 1-t 



to, 110, / 



The following are the measured and calculated angles. 



Calculated. Measured. 



to„to, 110/, 110 84° 59' 



a^m, 100/, 110 42° 29' 42° 36' 



j 001/, 110 86° 39' 86° 30' 



' (001/, 110 93° 21" 93° 40' 



C/,e, 001/, 011 48° 39' 48° 39' 



Two twin crystals were found. They were not very perfect 

 but the reentrant angle a /s a could be measured giving 9° 6', 

 calculated 9° 6'. 



It may be said of the measurements on the prism to, that the 

 face was usually quite imperfect and did not admit of very ac- 



* See beyond. f See beyond. 



