Blake — Columhite of the Black Hills, South Dakota. 405 





Measured. 



Calculated 



m* d. 110^730 



20° 



6' 



20° 5V 



m* z, 100 a 530 



13 



27 



13 12£ 



m*m, 110 a 110 



100 



39 



100 43 



a a /, 100 a 102 



61 



42 



61 46 



a * k, 100 a 103 



TO 



30 



70 18 



a a o, 100 a 111 



51 



18 



51 ]5£ 



a a u. 100 a 133 



74 



52 



15 1* 



a a n, 100 a 163 



79 



24 



80 3 



a a 7T, 100 a 121 



62 



14 



62 15 



The prism d, which is prominent on these crystals, is new to 

 the species. 



The crystals from the Etta Mine are to a great extent inde- 

 pendently formed and are thicker and stouter than those from 

 the Ingersoll. The largest crystal secured weighs several 

 pounds, and measures about 1J inch by 5 inches and is 4^ 

 inches long; another is 1^x3x3^; and a fragment of a larger 

 crystal is 2 inches thick and 4 inches long. Most of them are 

 detached from the gangue, or matrix, but one has portions of 

 beryl and quartz adhering to the side. 



The habit of the crystals is dependent upon a prominent devel- 

 opment of the pinacoicls a, 100, i-l and d, 010, i-i and the macro- 

 dome k, 103, •£■-£. Other faces which were observed are c, 001, O ; 

 m, 110, /; o, 111, 1 ; w, 133, 1-3 and n, 163, 2-6. The arrange- 

 ment of the planes is shown in fig. 3. The crystals were not 

 suitable for accurate measurement ; on the large crystals the 

 forms were identified by means of a contact goniometer, and 

 on a small crystal the following angles were measured on a 

 reflecting goniometer : 







Measured. 



Calculated. 



a a k, 



100 a 103 



70° 



70° 18' 



a a m, 



100 a 110 



39 28' 



39 38£ 



a a o, 



100 aIII 



51 20 



51 15| 



& a 72, 



010 a 163 



29 15 



30 50~ 



& A u, 



010 a 133 



49 15 



50 3 



The specific gravity determinations invariably show that 

 the Etta variety is the heavier of the two. The results upon 

 different crystals and fragments were as follows : 



From the Etta Mine. From the Ingersoll Claim. 



6-580 b 642 5-873 5881 



6-610 (6-447 Penfield.) 5-879 (5-901 Penfield.) 



A small tabular crystal found loose in the soil of Etta Hill 

 gave me 6171 and another from Spring Creek 6*132. Mr. 

 Headden's determinations of the specific gravity of the Etta 

 specimens range from 5*890 to 6*750, and for the Ingersoll 

 specimen he found 5*901. 



