Kleinite

Kleinite is a rare mineral that has only been found in the United States and Germany that occurs in hydrothermal mercury deposits.^[2] It occurs associated with calcite, gypsum and (rarely) barite or calomel.^[3] Its color can range from pale yellow/canary yellow to orange, and it is transparent to translucent.^[2] As a photosensitive mineral, its coloration darkens when exposed to light.^[4]

Kleinite
Kleinite atop quartz from the McDermitt Mine
General
Category	Minerals
Formula	(Hg2N)(Cl,SO4) · nH2O
Strunz classification	3.DD.35
Crystal system	Hexagonal
Crystal class	Dihexagonal dipyramidal 6/mmm (6/m 2/m 2/m)
Unit cell	a = 6.762(2) Å, c = 11.068(3) Å, Z=4
Identification
Color	Light to canary-yellow, orange
Crystal habit	Short prismatic to equant crystals exhibiting prominent {1010}, {2021}, and {0001}
Cleavage	Uneven on {0001}, imperfect on {1010}
Tenacity	Brittle
Mohs scale hardness	3.5
Luster	Adamantine to greasy
Streak	Sulfur yellow
Diaphaneity	Transparent to translucent
Specific gravity	7.9-8.0
Optical properties	Uniaxial (+) (Biaxial below 130 °C (biaxial negative) and uniaxial above 130 °C (uniaxial positive). Isotropic above ~ 190 °C)
Refractive index	nω = 2.190 nε = 2.210
Birefringence	δ = 0.020
Other characteristics	Color deepens on exposure to daylight, original color returns in darkness
References	[1][2]

It has been hypothesized that kleinite formed through a "reaction of cinnabar with oxidized meteoric water", with this reaction being the source of kleinite's nitrogen.^[4]

Etymology

Kleinite is named after Carl Klein (1842–1907), who was a professor of mineralogy at the University of Berlin.^[2]

• 
  Kleinite on calcite, from McDermitt Mine (Cordero Mine; Old Cordero Mine), Opalite District, Humboldt County, Nevada, United States

See also

• Halide minerals
• List of minerals