NO. 2351. NOTES ON METALLIC MINERALS— SHANNON. 599 



galena and tetrahedrite were used in the analysis. The bismuto- 

 plagionite is molded around both pyrite and quartz crystals. In 

 one small cavity between pyrite crystals the bismutoplagionite was 

 found to form small prismatic needles. 



PHYSICAL PROPERTIES. 



In appearance the new mineral is not distinctly different from 

 cosalite, galenobismutite, or many other sulphosalts of lead. The 

 color is slightly bluish lead-gray and the luster is rather dull metal- 

 lic. The aggregates are indistinctly fibrous, the fibers curving about 

 idiomorphic crystals of pyrite or quartz, which, when removed, leave 

 lustrous molds in the gray mineral. There are one or more ill-defined 

 cleavages parallel to the elongation of the fibers. In one instance the 

 bismuth mineral formed very minute free acicular crystals, extend- 

 ing across a minute cavity between pyrite crystals. These needles 

 were too minute for measurement, were not terminated, and were 

 deeply striated parallel to the elongation. The fibrous habit of the 

 massive material, the elongate striated needles, and the cleavages 

 parallel to the elongation unite to suggest that bismutoplagionite is 

 probably orthorhombic in crystallization. The streak of the mineral 

 is dull brownish-gray; the hardness 2.8 and the specific gravity 5.35. 



PTROGNOSTICS. 



Before the blowpipe alone on charcoal bismutoplagionite fuses to 

 a brittle globule and yields a coating which is yellow nearest the 

 assay (lead) and white in its outer portion (bismuth). With sodium 

 carbonate it is reduced to a metallic button, yielding similar coatings 

 on the coal. In the closed tube it yields sublimates of yellow sulphur 

 and black antimony sulphide. In the open tube abundant sulphur 

 dioxide is given off, and at a high temperature there is formed a 

 heavy sublimate, Avhich is yellow when hot and yellowish white when 

 cold. With potassium iodide-sulphur mixture a strong bismuth 

 reaction is obtained. 



CHEMICAL COMPOSITION AND PROPERTIES. 



It was quite impossible to obtain a sample for analysis which did 

 not contain pyrite, as the two minerals were found to be very inti- 

 mately mixed. Several lumps of the pyrite-bismutoplagionite aggre- 

 gate which, upon examination of polished surfaces, seemed to con- 

 tain no additional minerals, were crushed to an average grain of 

 2 to 3 millimeters. From this granular sample the purest grains of 

 the gray mineral were selected and each grain was examined with 

 a high-power lens without detecting any galena or other impurity. 

 This selected material was then ground and screened and used for 

 analysis. The sample contained abundant pyrite, but this occasioned 

 slight concern since preliminary tests had shown that the lead-bis- 



