Orange single crystal of the very rare mineral uzonite from the type locality in Uzon caldera (Uzon Caldera, Kamchatka Krai, Russian Federation). Ex Vandenbroucke Museum collection from Waregem, Belgium — Photo: David Hospital · CC BY-SA 4.0
Uzonite
Uzonite is an IMA-recognized mineral species in the sulfide class, with the chemical formula As₄S₅.
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 1.5; specific gravity 3.385; Pearly to slightly greasy on a broken surface luster; optically biaxial.
IMA symbol Uzn, IMA status: approved, named in 1984.
Occurs as intergrowths with realgar in the pore spaces of tuffaceous sediments 10–30 cm deep in a caldera.
It is found associated with Realgar, cubic α–arsenic sulfide, amorphous arsenic sulfide, orpiment, alacranite, stibnite, cinnabar, pyrite, sulfur.
The name is taken from the type locality, Uzon caldera, Russia.