G. J. Brush—American Sulpho-Selenides of Mereury. 315 
rence of native mercuric sulpho-selenides, which, thus far, I 
believe, have only been found on the North American conti- 
nent. The first mention of a native sulpho-selenide of mercury 
is by Del Rio.* He found at Culebras, in Mexico, in a lime- 
stone which overlaid red sandstone, two ores, one red and the 
other gray ; the former he described as ‘‘biseleniuret of zine 
and bisulphuret of mercury,” and the latter a “ biseleniuret 
of zine and sulphuret of mercury.” The English mineralogist, 
Brooke, named the red mineral culebrite, after the locality, and 
the gray mineral riolite,t in honor of its discoverer. e gray 
mineral had a density of 5°56, and, according to Del Rio, con- 
tained Se 49, Zn 24, Hg 19, S 1: 
ongjrite.| This mineral was found in compact granular masses, 
associated with calcite and barite, and, according to Mr. C. 
Ehrenberg, one of the officials of the Real del Monte Com- 
pany, the mineral occurred in such quantity that it was ge 
og to use it as an ore of mercury, although Rose had so 
ittle of the mineral for examination that he was unable to 
detach a sufficient amount of it from adhering barite to enable 
him to ascertain its specific gravity. : 
n 1865, Professor A. del Costillo, of Mexico, described** a 
sulpho-selenide of zine and mercury from the quicksilver mines 
of Guadaleazar; this mineral was subsequently independently 
examined and analyzed by Petersen¢t+ and named guadal- 
cazarite. A more recent analysis of the same mineral is given 
by Rammelsberg in his Mineralchemie, p. 79. These minerals 
bear a close resemblance to one another in physical characters, 
48 well as in chemical composition, as will be seen by the table of 
* Phil. Mag. and Ann. Phil, vol. iv, (1828) p. 113. ; 
t Rionite is another name given by some authors for the same mineral. 
¢ L. and K. Phil. Mag., vol. viii, (1836) p. 262. 
arn Archiy., xiv, 27. 
__| In Dana’s Mineralogy, 5th ed., p. 56, line 10 from bottom of page. the density 
Siven by Del Rio for his gray mineral is erroneously attributed to onofrite. 
Dana Min., 5th ed., p. 109, and Burkhardt, Jahrb. Min., 1866, p. 414. 
tt Tschermak, Min. Mittheil., 1872, p. 69 and p. 243. 
