Rosickýite

Rosickyite is a rare native element mineral that is a polymorph of sulfur. It crystallizes in the monoclinic crystal system and is a high temperature, high density polymorph. It occurs as soft, colorless to pale yellow crystals and efflorescences.[1][2]

Rosickyite
Sharp yellow crystals of rosickyite on matrix from an unspecified off shore drill hole in the Pacific Ocean near California (Ventura County, California, United States of America).
General
Category	Native element mineral
Formula (repeating unit)	S
Strunz classification	1.CC.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P2/c
Unit cell	a = 8.455(3) Å, b = 13.052(2) Å c = 9.267(3) Å; β = 124.89(3)°; Z = 4
Identification
Color	Colorless to pale yellow, green tinge
Crystal habit	Equidimensional to thin tabular crystals, efflorescences
Twinning	On {101}, with twin lamellae parallel to [010]
Cleavage	None
Mohs scale hardness	2 - 3
Luster	Adamantine
Diaphaneity	Transparent to translucent
Specific gravity	2.07
Optical properties	Biaxial (-)
References	[1][2][3]

It was first described in 1930 for an occurrence in Havirna, near Letovice, Moravia, Czech Republic. It was named for Vojtĕch Rosický (1880–1942), of Masaryk University, Brno.[1][2]

Rosickyite occurs as in Death Valley within an evaporite layer produced by a microbial community. The otherwise unstable polymorph was produced and stabilized within a cyanobacteria dominated layer.[4]