NO. 2351. NOTES ON METALLIC MINERALS— SHANNON. 605 



the " iron dike " argentite and ruby silver were found in nuggets em- 

 bedded in clay, and small streaks of whitish kaolin, strongly impreg- 

 nated with argentite, were also rich in gold. Some clayey streaks in 

 the hanging walls of veins elsewhere in the mine are also rich in argen- 

 tite, although as a whole the mine is predominantly a gold mine. The 

 minerals of the vein include native gold, argentite, and ruby silver, 

 and, near the surface, some cerargyrite.^ The ruby silver of this mine 

 is largely miargyrite. The specimen of naumannite described below 

 was supposed to be typical of the larger nodules of argentite occurring 

 in the clay seams. To what extent the so-called argentite consisted of 

 naumannite is not known, but it is far from impossible that nearly all 

 of the abundant nuggets and streaks of so-called silver sulphide 

 which occurred in kaolin in this mine may have been naumannite. It 

 is to be hoped that other specimens of these ores can be secured for 

 examination. 



PHYSICAL PBOPEETIES. 



The specimen is an irregular flat rectangular nodule about 10 by 

 7 by 3 centimeters in maximum dimensions and weighing about 475 

 grams. Little of the metallic mineral was visible on the exterior of 

 the nodule, which was completelj^ coated with a tenacious layer of 

 grayish clay. The interior of the nodule consists of the heavy 

 metallic mineral which is so tenacious and malleable that projecting 

 corners are broken from it with difficulty. On broken surfaces it is 

 seen to have a hackly fracture and dark blue-gray color. The luster 

 is metallic, and the surface, upon exposure, does not become appre- 

 ciably dulled, nor does it assume the furred appearance characteristic 

 of argentite. When polished sections are examined under the micro- 

 scope with vertical illumination the mineral is seen to be pure except 

 for the clayey matter which is scattered in grains and small patches 

 throughout the mass, and marcasite, which forms small disseminated 

 points in the silver mineral. The hardness is about 2.5. The streak 

 on paper is dark brownish gray ; on porcelain, gray, faintly shining. 

 A specific gravity determination on fragments containing 5 or 6 per 

 cent of clay gave the value 6.527. 



PTROGNOSTICS. 



Heated before the blowpipe on charcoal the mineral yields selenium 

 immediately, and colors the flame blue with the production of the 

 characteristic selenium odor, leaving a large mass of malleable silver. 

 In the closed tube it gives odors of sulphur and selenium, and yields 

 a series of sublimates in rings which grade from yellow (sulphur) 

 at the top, through red (selensulphur) , to deep red and black (sele- 

 nium). In the open tube there are obtained odors of sulphur, and 



1 Llndgren. W., U. S. Geol. Survey, Ann. 20, pt. 3, p. 127, 1900. 



