380 Allen and Crenshatc—$ul]>hid<x of Zinc, 



The black coating should be thicker here if our explanation is 

 correct, but the grinding process might well give a powder of 

 a redder hue. We found, in accord with this supposition, that 

 a verv pure vermilion powder (unsublhned cinnabar) also gave, 

 on heating, a product which was considerably darker after it 

 was ground than a product formed by heating coarser cinnabar. 



Whether our explanation be correct or not, it remains cer- 

 tain that metacinnabar and the new /3'-HgS are both mono- 

 tropic forms, while cinnabar is stable. 



Genetic conditions of the natural mercuric sulphides. — 

 The evidence for the geologic view that cinnabar is a product 

 of alkaline solutions is convincing. The close and constant 

 association of the mineral with igneous rocks is significant, 

 while in two well-known localities, Steamboat Springs, NeV.,* 

 and Sulphur Bank, Cal., it seems to be in the process of depo- 

 sition from alkaline waters at the present day. Posepnyf states 

 that in the former locality pyrite is apparently forming with 

 it. Cinnabar is thus undoubtedly a primary mineral. In some 

 cases also it appears to be secondary, since mercurial tetrahe- 

 drite oxidizes readily to sulphates, and the descending solution 

 seems to be precipitated as cinnabar on other sulphides at 

 lower levels (Lindgren). Metacinnabar, on the other hand, is 

 regarded as a characteristic secondary mineral. It was found 

 near the surface in the Knoxville district, Cal., and has not 

 been found lower down. A large part of the ore in the Baker 

 Mine and in the upper levels of the Beddington Mine were 

 metacinnabar.;}; Melville§ describes an occurrence of meta- 

 cinnabar in the New Almaden mines, Santa Clara Co., Cal., 

 where cinnabar and quartz are intimately mixed, while meta- 

 cinnabar is crystallized on the quartz and is "certainly subse- 

 quent to it." 



The metacinnabar of Idria, according to Schrauf, || is far 

 younger than the cinnabar which underlies it and has appar- 

 ently been formed since the opening of the mines. It occurs 

 here in hemispherical crystal aggregates which suggest to 

 Schrauf that they may have formed by the action of hydrogen 

 sulphide on the globules of metallic mercury which invariably 

 accompany the cinnabar. Schrauf refers here to the experi- 

 ments of Fleck, which lead him to believe that the metacinna- 

 bar formed in the presence of sulphuric acid. It is a note- 

 worthy fact that metacinnabar is commonly associated with 

 marcasite, at least in this country.! 



* W. P. Blake, this Journal (2), xvii, 438, 1854. 

 f Trans. Min. Kng., p. 228, 1893. 

 % Becker, TJ. S. G. S. Monograph 13, p. 284. 

 § This Journal, xl, 293, 1890. 



j Ueber Metaeinnabarite von Idria und dessen Paragenesis. Jahrb. der 

 k. k. geolog. Reiehs., xli, p. 379-399, 1891. N. J. Min. 1893, I, referate 465. 

 *[ Becker, loc. oit., p. 285. Penfield, this Journal, xxix, 452, 1885. 



