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University of California Publications in Geology [Vol. 13 



Polydymite. — The nickel-bearing mineral of the massive ore can be seen only 

 on polished surfaces. It is white in color, takes a fair polish, and is 5.0 to 5.5 

 in hardness. This mineral has good cleavages in three directions, which have 

 been interpreted as cubic. See plate 10, figures 5 and 6. 



Following are the results of michochemical tests of this mineral: 



HN0 3 dilute — slight, dull brown stain, rubs to clean smooth surface. 



HNO3 cone. — strong effervescence, dark brown stain. Eubs to gray rough- 

 ened surface. 



HC1, both dilute and concentrated — acid turns yellow. 



Aq Eeg. — strong effervescence, light brown stain, rubs clean. Acid turns 

 green. 



FeCl 3 — no effect. 

 NH 4 OH — no effect. 



KCN — slight brown stain, rubs clean. 



This mineral does not correspond exactly in its chemical reactions to any 

 of the minerals listed in Murdoch's tables. 22 Chloanthite, gersdorfite, and 

 polydymite are suggested by the determinative tables, the description of gers- 

 dorfite perhaps corresponding closest to the Friday Mine mineral. However, 

 blowpipe analysis of isolated fragments of the pure mineral and also of the 

 whole ore show no trace of arsenic, giving strong tests for nickel and sulphur, 

 with no cobalt. 



It is concluded that this mineral is either polydymite or a closely allied and 

 hitherto undescribed species. 



Brown Hornblende. — This mineral, differing in no way in optical properties 

 from that found in the gabbros and norites, is to be found in samples of the 

 least altered ore. It occurs in euhedral and subhedral forms, inclosed within 

 single pyrrhotite crystals or in the spaces at the meeting point of several 

 crystals. The brown hornblende of the ore has a much greater tendency toward 

 euhedral outline than does that of the norites and gabbros. This is well shown 

 in plate 10, figures 3 and 4. 



Compact Green Hornblende. — This mineral is much like the brown variety in 

 its mode of occurrence. It is pleochroic in green and blue-green colors. 



Augite. — A small amount of colorless pyroxene with positive sign was iden- 

 tified in the ore from the lower mine level. Some of the more altered ore from 

 the upper level shows under the microscope six and eight sided masses com- 

 posed of granular caleite. These are thought to be pseudomorphs of the car- 

 bonate after augite. 



Chlorite. — Green clinochlore occurs in greater or lesser amount in all the ore. 

 It is found replacing the hornblende and also as minute veinlets traversing both 

 the silicates and ore minerals. Plate 10, figure 3 illustrates the partial replace- 

 ment of brown hornblende by chlorite. 



An inspection of thin sections and polished surfaces leaves no doubt that 

 the chlorite in both its modes of occurrence was introduced at a distinctly later 

 time than that of the formation of the sulphides and hornblende. In the com- 

 pletely oxidized gossan the chlorite is found in hexagonal tablets with good 

 crystalline outline. These may attain a diameter of one-half inch. In the 

 partially oxidized ore chlorite occurs in a similar way, but in the fresh ore it is 

 found only in small individuals replacing the hornblende and in the minute vein- 

 lets cutting the ore minerals. This evidence suggests that the chloritic type of 



22 Murdoch, Joseph, Microscopical determination of the opaque minerals 

 (New York, 1916). 



