Selenium (Se) is # 34 on the Periodic Table of Elements. Elemental selenium is a nonmetal that varies in its appearance, from gray to red to black. Native sel — Photo: James St. John · CC BY 2.0
Selenium
A non-metal (symbol Se, atomic number 34) occurring natively as red or gray metallic-looking forms — a semiconductor used in electronics.
Intro adapted from Wikipedia (CC BY-SA).
Selenium is an IMA-recognized mineral species in the native element class, with the chemical formula Se.
It crystallizes in the hexagonal crystal system (space group P3_221). It is a member of the Sulphur structural group.
Key properties: Mohs hardness 2; specific gravity 4.8; typically gray or red; Red streak; Metallic luster; optically uniaxial.
IMA symbol Se, grandfathered status — known before the IMA’s founding, named in 1934.
Formed at relatively low temperatures by sublimation of fumarolic vapors, and from oxidation of selenium-bearing organic compounds in sandstone U–V deposits; from burning coal and pyritic ores.
It is found associated with Pyrite, ferroselite, zippeite, metatyuyamunite, metarossite, montroseite, corvusite.
The name comes from the Greek, selene, the moon, in allusion to its similarity to tellurium, named for the earth, Latin tellus.
Collections: Rare & Remarkable.