kleinite

{{Infobox mineral | name = Kleinite | boxwidth = | boxbgcolor = | image = Kleinite-21676.jpg | imagesize = 260px | alt = | caption = Kleinite atop quartz from the McDermitt Mine | category = | formula = (Hg2N)(Cl,SO4) · nH2O | strunz = 3.DD.35 | dana = | system = Hexagonal | class = Dihexagonal dipyramidal 6/mmm (6/m 2/m 2/m) | symmetry = | unit cell = a = 6.762(2) Å, c = 11.068(3) Å, Z=4 | color = Light to canary-yellow, orange | habit = Short prismatic to equant crystals exhibiting prominent {100}, {201}, and {0001} | twinning = | cleavage = Uneven on {0001}, imperfect on {100} | fracture = | tenacity = Brittle | mohs = 3.5 | luster = Adamantine to greasy | streak = Sulfur yellow | diaphaneity = Transparent to translucent | gravity = 7.9-8.0 | density = | polish = | opticalprop = Uniaxial (+) (Biaxial below 130 °C (biaxial negative) and uniaxial above 130 °C (uniaxial positive). Isotropic above ~ 190 °C) | refractive = nω = 2.190 nε = 2.210 | birefringence = δ = 0.020 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = Color deepens on exposure to daylight, original color returns in darkness | prop1 = | prop1text = | references = }}

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