220 QUARTZ FAMILY. The internal lustre is glistening, and resinous. 1 he fracture is large and flat, but sometimes imperfect Conchoidal. The fragments are angular, and very sharp edged. It is generally translucent on the edges; some varieties are translucent. It is easily frangible. It is hard ; but softer than calcedony. It is rather heavy. Specific gravity, 2.623, Karsten. 2.700, KirwaV- 2.614, Hoffmann. 2.633, Blumenbach. Chemical Characters. It is infusible before the blowpipe. # Constituent Parts. n Silica, - 84.00 Alumina, 7.50 Iron, - 5.00 Tromsdorf. Gcognostic Situation. It is found in rocks belonging to the floetz-trap forma tion, and probably occurs in the same kind of repository as calcedony. Geographic Situation. The ancients procured this mineral from Ethiopia* At present, the most highly esteemed varieties are brought from Bucharia, Great Tartary, and Siberia. It occurs also in Iceland; and it is said also in Transilvania, Sar dinia*