One outstanding grey brown single group of whitish microcrystals of the extremely rare selenium dioxide mineral downeyite from one of the only two known localities worldwide , both In Pennsylvania (Burnside, Northumberland County, Pennsylvania, United States of America). Downeyite (SeO2) is a mineral of very simple chemistry but it is extremely rare worldwide, even more in analyzed specimens by SEM/EDS like this one. Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Downeyite
Downeyite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula SeO₂.
It crystallizes in the tetragonal crystal system (space group P4_2/mbc).
Key properties: specific gravity 4.165; Adamantine luster; optically uniaxial.
IMA symbol Dny, IMA status: approved, named in 1974.
Found as a rare sublimation product of gases escaping through vents in actively burning culm banks in anthracite coal deposits; forms at about 200 ° C near the vents.
It is found associated with Selenium, rosickýite, mascagnite.
The name refers to Wayne F. Downey, Jr., of Harrisburg, Pennsylvania, USA, who first collected the mineral.