THE MINERALS OF IDAHO 383 



This analysis may be compared with many analyses of prochlorite 

 given by Dana. The formula yielded by the ratios is 9 (Mg,Fe) 

 0.3Al 2 3 .5Si0 2 .7H 2 0. 



Other similar occurrences of fine-grained chlorites have been noted 

 in other veins in the Coeur d'Alene region. They are nowhere con- 

 spicuous. 



SERPENTINE (669) 



Hydrous magnesium silicate, Monoclinic. 



3M g 0.2Si0 2 .2H 2 0. 



Although a common mineral elsewhere, serpentine has seldom been 

 reported from Idaho, possibly having been overlooked because of its 

 inconspicuous appearance and lack of commercial value. The follow- 

 ing localities are known: 



ADAMS COUNTY 



Antigorite, the lamellar or platy variety of serpentine has been 

 listed from the Seven Devils district by Livingston and Laney. 91 



BLAINE COUNTY 



Specimens from the Queen of the Hills Mine IK miles west of 

 Bellevue (Cat. No. 78,524 U.S.N.M.) consist of a fibrous mineral 

 labeled asbestos, associated with calcite and fragments of sheared 

 black slate. The asbestiform mineral is apparently fibrous serpentine. 

 The calcite is in part in white cleavable granules embedded in the 

 serpentine and is in part fibrous. The serpentine is pale buff in color 

 and forms parallel-fibrous masses the fibers of which bulge around 

 included calcite and are crumpled somewhat at the ends. The 

 fibers reach a length of 11 cm. and individual masses are 5 cm. in 

 breadth. The material has a harsh dry feel and little luster. The 

 fibers are not easily separable and are more or less brittle. No 

 analysis of the mineral has been made, but it is identified as chrysotile 

 by its optical properties. In thin section under the microscope it is 

 pale greenish brown to brown and is pleochroic, the color being more 

 pronounced parallel to the fibers. The extinction is parallel, the 

 elongation positive. The refractive indices vary somewhat but 

 average a =1.50, 7=] .52. 



CUSTER COUNTY 



Serpentine is a meager constituent of the copper-bearing deposits 

 of the Alder Creek district, where it occurs as an alteration product 

 after hornblende and diopside. In a raise from the north Alberta 

 stope to the 300 foot level a band of serpentine with intermixed 

 quartz and malachite follows the fault plane. This layer is about 2 

 inches wide and shows evidence of much shearing. 92 The serpentine 



•1 D. C. Livingston and F. B. Laney. Idaho Bur. Mines and Geol., Bull. 1, p. 62, 1920. 

 « J. B. Umpleby. U. S. Geol. Survey, Prof. Paper 97, p. 54, 1917. 



