S. fchikawa — Some Notes on Japanese Minerals. 119 



a. Concentric radial aggregates about the principal axis of 

 the rhonibohedron forming a sphere, this form has long been 

 known by the name of " konpetoishi," they measure 10 to 15" Hn 

 in diameter (fig. 1.) 



b. Parallel growth of numerous rhombohedrons forming 

 cube-like forms, measuring 5 to 10 mni in diameter (fig. 2.) 



e. Complex penetration-twins of four individuals of the b 

 type, of many interesting forms, measuring 5 to 10""" in 

 diameter (tigs. 3 to 10.) 



cl. Irregular-aggregates of the individuals of b measuring 20 

 to 30 mm in diameter. 



Simple rhombohedral crystals, 3 to -± mm in diameter, were 

 also found attached to the vein-stone. In the above crystal- 

 aggregates, a and cl are found more frequently than b, but the 

 b type is very rare. 



When fresh, the arsenic is tin-white, but after half a clay 

 it is gradually tarnished to a dark color, and after six months 

 becomes dark-gray by oxidation. "When decomposed by long 

 exposure to the air, the spherical aggregates sometimes natu- 

 rally reveal the concentric zonal structure in their fracture, 

 and the spongy structure in their outer part. 



The crystal-aggregates, especially the irregular forms, some- 

 times enclose stibnite and minute crystals of pyrite ; this is espe- 

 cially common with the irregular forms. Some specimens are 

 also colored by orange-yellow realgar. 



The microscopical structure in the fracture of spherical 

 aggregates or complex penetration twins shows innumerable 

 cleavages in the layers of the concentric zonal structure much 

 resembling that of the bulb of a lily (ex. fig. 12.) 



Native arsenic (so-called " konpetoishi ") is said to have been 

 recently observed also, in Kochi, Kawada-mura, Imatate-gun 

 near the Akadani-mine. 



The above papers, with the accompanying illustrations, were 

 presented to the Twelfth International Geological Congress in 

 Toronto, Canada, in August, 1913. 



Kitashinjo-rnura, lmitate-gun, Fukui-ken, Japan. 



