THE MINERALS OF IDAHO 



293 



approximating those of the varieties of amphibole which hare been 

 called hudsonite and hastingsite. 



The specimen consists mainly of the amphibole which forms 

 imperfect glistening black prisms up to 5 cm. in length by 2 cm. 

 broad. These have very well defined cleavage. They are associated 

 with a little diopside and calcite, and the appearance of the specimen 

 suggests that it came from a crystalline limestone. Under the 

 microscope the amphibole is very deep colored and is transparent 

 only in thin splinters. It is biaxial and negative with 2V small; 

 extinction Zac = 23°-37°; refractive indices a = 1.695, 0= 1.702, 

 7 = 1.712; birefringence, y-a = 0.017. The pleochroism is intense, 

 X = Greenish-brown, Y = Brownish-green, Z = Smoky blue-green. 

 Absorption Z>Y>X. 



A selected sample, purified by the use of heavy solutions and an 

 electromagnet, was used for anatysis. Microscopic study indicated 

 the presence of 4 per cent of diopside in the analyzed sample. The 

 results of the analysis are below compared with analyses of hudsonite 

 and hastingsite. 



Analyses of hudsonite and related low-magnesia amphiboles 



Constituent 



(1) 

 Idaho 



(2) (3) 



Hudson- ! Hastings- 

 ite ite 



Silica (SiOs) 



Titanium oxide (Ti02) 



Alumina (AI2O3) 



Ferric iron (Fe203) --. 



Ferrous iron (FeO) 



Manganous oxide (MnO)_. 



Lime (CaO) 



Magnesia (MgO) 



Soda(NajO).. 



Potash (KsO) 



Water (H 2 0) above 110° C 

 Water (H 2 0) below 110° C 



Total 



38.50 



Trace. 



10.88 



6.70 



27.28 



Trace. 



11.30 



1.40 



1.22 



1.66 



1.27 



None. 



36.86 



1.04 



12.10 



7.41 



23.35 



.77 



10.59 



1.90 



3.20 



1.20 



.60 



.70 



34.18 



1.53 



11.52 



12.62 



21.98 



.63 



9.87 



1.35 



3.29 



2.29 



.35 



100.21 



9.72 



99.61 



(1) Amphibole from Custer County, Idaho. E. V. Shannon, analyst. Manganese and titanium were not 



estimated but were colorimetrically shown to be unimportant. 



(2) Hudsonite, Cornwall, Orange County, N. Y. J. L. Nelson, analyst. S. Weidman, Am. Jour. Sci., 



vol. 15, p. 231, 1903. 



(3) Hastingsite, Ougannon, Ontario. Adams and Harrington, Amer. Jour. Sci., vol. 1, p. 213, 1896. 



The Idaho material is nearer hudsonite in composition and hence 

 may be designated by this varietal name until the character and 

 relationships of these minerals are satisfactorily interpreted. 



BERYL (344) 



Beryllium-aluminium silicate, 3BeO.- Hexagonal. 



Al 2 3 .6Si0 2 . 



Only two occurrences of beryl have thus far been reported from 

 Idaho. 



