Geology and Mineralogy . 



165 



Meas. 



Calc. 



Meas. 



L09° 50' 



100 a 403 = 64° 29' 



64° 14' 



35 26 



100 a 111 = 69 4 



69 13 



50 50 twin 



111 a 111=41 52 



41 57 



29 54 



001 a 111 = 75 11 



75 27£ 



63 25 



001 a 221 = 89 42 



89 54 



in the direction of the ortho-axis, that of Pike's 

 Peak shows a prismatical development. It occurs 

 with calcite on a base of altered pyroxene or am- 

 phibole. The crystals are 2-5 mm in length and 

 breadth, and though the planes do not allow of 

 accurate measurements, the latter are sufficient to 

 identify the planes. The figure shows the habit 

 of the crystal, which is a twin, with a as the twin- 

 ning plane. The planes identified are a (100, T), 

 c (001, M), «(210), m(110, z of most authors), 

 e(101), £(102), N (304), r (101), I (201), n (111), 

 q (221). Some of the measured angles are : 



Calc. 

 110 a 110 = 109° 56' 



100 a 210= 35 29£ 

 001 a 001= 50 46" 



101 a 100= 30 23 

 100 a 101= 63 42 



Hajstksite. — A pyramidal crystal with polished planes, and in 

 habit resembling figure 1 on p. 66 of the last volume of this 

 Journal, gave the axial ratio a:c=l : 1-00564, and the following- 

 measurements : 



Meas. Calc. Meas. Calc. 



oo (pyr.)=*44° 31' mo=67° 44' 67° 44£ 



co = 49 15£ 49° 16' ms=23 12 23 ltj 



With HC1 the substance effervesces ; the solution tested with 

 BaCl„ gave only a comparatively small precipitate of BaS0 4 . A 

 new chemical investigation of the bright crystals may therefore 

 be necessary. The only one in my possession is not pure enough 

 for a chemical analysis. 



5. Plattnerite from Idaho;* by J. D. Hawkins and Edwin N". 

 Hawkins. (Communicated). — In the early part of June, Mr. A. 

 Chanute, Vice-President of the Globe Smelting and Refining 

 Co., collected a specimen of plattnerite from the " As You 

 Like " Mine, near Wallace, Shoshone Co., Idaho, which he gave 

 to us for examination and analysis. The specimen, of the size of 

 a large duck's egg, was superficially coated with limonite, and 

 was of a nodular structure ; color iron-black, streak chestnut- 

 brown. The fracture was uneven, and showed a dense structure ; 

 hardness between 5-5 and 6, fusibility 2, and very easily reducible 

 to metallic lead. The mean of three close determinations of the 

 specific gravity of the mineral in powder was 7*25. This specific 

 gravity seems to be more in accordance with the specific gravity 

 of Massicot (8-0) than that given by Wheeler (9-46). Two anal- 

 yses, on 1 and 0*5 grams respectively gave the following results : 



Pb0 2 9099 91-03 



ZnO -07 (07) 



J Si0 2 2 -6 1 



| A1„0, -2i 

 Fe 2 3 5-69 



Insoluble in HCL. 2'96 



3-00 



99-71 99-96 



* Compare p. 79 of the July number. 



