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Account of a new species of Mineral named Poli/basite, and 

 Observations onJZinkenitc. 



Xhis mineral has been hitherto confounded with tlie Sprodgla- 

 serz, but is distinguished from it by form and composition. 

 Rose was the first to point out the difference of this species from 

 Sprtidglaserz, and communicated to his brotlier H. Rose the 

 following observations : — The crystals of this new species are 

 regular six-sided prisms, vvhich are commonly low and tabular, 

 and terminated on the ends by planes perpendicular to the axis 

 of the prism. The lateral planes are transversely streaked, and 

 meet under 120°. The planes perpendicular to the axis are 

 streaked in a direction parallel to the planes of an equilateral 

 triangle, or parallel to the alternate terminating edges of the six- 

 sided prism. Hence it follows, that the crystal must be rhom- 

 boedral. The fracture is uneven. The crystals are iron black ; 

 lustre splendent both on the fracture and external surfaces. 

 Colour not changed in the streak. It is sectile ; hardness be- 

 tween that of rock salt and calcareous spar. Specific gravity of 

 a variety from Durango in Mexico is = 6.21 4, at temperature 

 of 10°'5. R. 



The Polybasite occurs partly in superimposed crystals, partly 

 massive and disseminated. It occurs in veins in the mines of 

 Guanaxuato in Mexico ; also at Guarisamey in Durango, in 

 the same country, with crystallized copper pyrites and calcare- 

 ous spar ; and also with stilbite, as at Andreasberg in the 

 Hartz. Probably the six-sided tables, streaked on the terminal 

 planes, from the mine Morgenstern near to Freyberg, belong 

 to this species. 



Werner's description of Sprodglaserz includes two six-sided 

 prisms ; one, which, when carefully examined, as has been done 

 by Mohs, proves to be an oblique four-sided prism, with 

 truncated acute lateral edges, and this is the Sprodglaserz of 

 Mohs ; the other, which is a i*egular six-sided prism, is the pre- 

 sent species the Polybasite. The Polybasite of Guarisamey, 

 in Durango, in Mexico, affords the following constituent parts : 



Sulphur, 17.04; antimony, 5.09; arsenic, 3.74; silver, 

 64.29; copper, 993; iron, 06 = 100.15. The portions of 



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