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G. J. Brush—American Sulpho-Selenides of Mercury. 318 
berry, he very kindly requested me to make a further investi- 
gation of the mineral, and placed in my hands an abundance 
of material for a quantitative examination. He stated that it 
occurs in what seems to be a fissure vein in a limestone, which 
he regards as paleozoic, and that the selenide was found at the 
toga of a thirty-foot shaft, forming a seam about four inches 
ide 
Physical properties.—The specimens received from Dr. New- 
berry were, with a single exception, small irregular fragments, 
free from rock. The larger specimen was in a gangue of com- 
pact gray limestone, but the greater part of the specimen, 3 by 8 
inches square and an inch in thickness, consisted of the sulpho- 
selenide. Even the limestone was found impregnated with the 
same, sometimes in visible specks, while in other portions of 
the rock it was not to be seen until acted upon by acid, or vola- 
tilized by heat in the closed tube. A small amount of associ- 
ated crystalline calcite also included minute particles of the 
metallic mineral. The most careful scrutiny of the gangue 
failed to discover any native metallic mercury, or other associ- 
ated metallic mineral, and there was no difficulty in selecting 
an abundance of the pure mineral for analysis entirely free 
from the gangue, 
_The mineral has a blackish gray color and streak. It has no 
distinct cleavage, but breaks with a conchoidal fracture and 
shows a brilliant metallic luster on freshly broken surfaces. 
The irregular natural surfaces of the specimens in my posses- 
Sion are somewhat spongy or cavernous in aspect, but afford 
no clue to the crystalline form of the mineral. The hardness is 
adout 2°5 and the specific gravity of the mineral, boiled in 
water to free from air, gave the figures 7°61 and 7°63, in two 
determinations. ‘ 
‘Yrognostics,—In the closed tube the mineral decrepitates at 
first, then volatilizes for the most part, gives reactions for sul- 
phur and mercury, coats the tube with a grayish black subli- 
cury and sulpho-selenide of mercury, and leaves, as before, a 
slight residue of a yellow color. On charcoal in R. F., the 
