292 W. H. Melville — Metacinnabarite from California. 



genesis of this metacinnabarite was certainly subsequent to the 

 deposition of the cinnabar, and groups of fiat rhombohedrons 

 of white semi-transparent calcite appear to have formed at the 

 same time. Crystallized dolomite is common among the ores 

 of New Almaden and to this a fibrous silicate, undoubtedly 

 chrysotile, firmly adheres. Fine bluish opal and occasional 

 spangles of pyrite complete the list of associated minerals. 



One other brittle substance was discovered while picking 

 out metacinnabarite for analysis. It forms almost perfect 

 spheres of a brilliant black color, which volatilize at a high 

 temperature in yellowish vapor with a strong bituminous odor. 

 The substance is organic matter and curiously mercury does 

 not enter into its composition. These spheres can be detected 

 under the microscope imbedded in the faces of the crystals of 

 metacinnabarite (fig. 2.) and some were obtained by sharply 

 rapping the specimen. 



The rather low specific gravity of metacinnabarite is thus 

 accounted for in part. Again the presence of minute particles 

 of quartz was unavoidable, and therefore the given value was 

 also influenced to a slight extent by this cause. The crystals 

 used for the determination of the specific gravity contained 

 far less impurity than is recorded in the analysis which follows. 

 The specific gravity was in two cases 7*095 and 7" 142, or mean 

 = 7*118 almost identical with that of guadalcazarite, 7'15. 



Analysis of Metacinnabarite. 



At. Ratio. 



S 13-68 0-855 



Hg 18-01 S corresponding=12-48# 0-7801 



Fe... 0-61 0-34 00218^ 



Co trace U-0549 



Zn 0-90 0-44 00277 f uuo * y 



Mn 15 0-09 0-0054J 



CaCOs 0-71 l1U5 



Residue, quartz 4-57 S found .13-68 



Volatile organic matter 0-63 



99-26 



For analysis - 6237 gram of substance was available, and 

 both the qualitative and quantitative study proceeded contem- 

 poraneously. The small errors of analysis are distributed 

 between the sulphur and organic matter, where the sulphur is 

 as usual a trifle too high An uncertainty naturally exists in 

 •the determination of the organic matter. Selenium was looked 

 for but its presence failed to be established. 



The crystals belong to the rhombohedral system (Miller) and 

 consist of two poles differently modified. The following 

 forms were observed : 



