154 SELE1TTDES. Is found in granular masses at Tilkerode and Zorgo in the Harz, under the same circumstances as Clausthalite, in the Eriedrichsgliick mine in Glasbachgrund near Gabel in Thu ringia, in a vein in clay slate. 45. EIOLITE.—Eiolith; Haidinger. Ehombohedral. Lead-grey. Very malleable. AgSe 2 , silver 57'66, selenium 42'34, according to Del Eio. Is found in small six-sided tables, with rounded edges and angles, at Tasco in Mexico. 46. OINTOI’EITE.—Selenschwefelquecksilbcr ; Hausmann. Onofrit; Haidinger. Lustre metallic. Blackish lead-grey. Streak shining. Sec- tile. h = 2’5. In the matrass sublimes undecomposed as a black powder; with soda yields metallic mercury. Before the blowpipe emits the smell of sulphurous acid. HgSe,HgS, a mixture of seleniuret and sulphuret of mer cury. Analysis by II. Eose :— Mercury . . . .81-33 Sulphur .... 10-30 Selenium . . . .6 49 Is found massive in veins with mercury, quartz, calcite, ba ryte, at San Onofre in Mexico. We quote the descriptions of onofrite and riolite as they are given by Haidinger; but we entertain considerable doubt of their correctness. Mr. Brooke has specimens of a metallic looking mineral said to have been found in the Culebras mine, and described by Del Eio in a letter to Mr. Brooke as ‘ native selenium with some admixtures,’ and to which Mr. Brooke, many years since, gave the name of riolite. Being desirous of ascertaining the difference between this mineral and onofrito, he obtained a specimen under this latter name from Mr. Krantz, which so perfectly resembles that referred to by Del Eio, as to leave no doubt of its being the same mineral, and from the same mine. The riolite of Haidinger, from Tasco, is described apparently on the authority of Del Eio; but it does not appear from what work that authority is quoted; and as no such compound is