johannite

{{Infobox mineral | name = Johannite | category = Sulfate mineral | boxwidth = | boxbgcolor = | image = Johannit - Ronneburg.jpg | imagesize = 260px | alt = | caption = | formula = Cu[UO2(OH)SO4]2·8H2O | IMAsymbol = Jh | molweight = | strunz = 7.EB.05 (10 ed) VI/D.21-10 (8 ed) | dana = 31.8.2.1 | system = Triclinic | class = Pinacoidal () (same H-M symbol) | symmetry = P | color = Emerald-green, apple-green | colour = | habit = Prismatic, tabular, coatings | twinning = Simple and repeated lamellar twinning | cleavage = good on {100} | fracture = | tenacity = | mohs = 2 - 2.5 | luster = Vitreous | streak = Pale green | diaphaneity = Transparent, Translucent | gravity = 3.32, 3.27 (calc.) | density = 3.32 | polish = | opticalprop = Biaxial (+/-) | refractive = nα = 1.572 - 1.577 ; nβ = 1.592 - 1.597 ; nγ = 1.612 - 1.616 | birefringence = δ = 0.040 | pleochroism = strong: x= colorless; y= pale yellow; z= greenish yellow or canary-yellow | 2V = 90° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = | other = 25px Radioactive, Bitter taste | alteration = | references = }}

Johannite is a rare uranium sulfate mineral. It crystallizes in the triclinic crystal system with the chemical composition Cu[UO2(OH)SO4]2·8H2O. It crystallizes in the triclinic system and develops only small prism or thin to thick tabular crystals, usually occurs as flaky or spheroidal aggregates and efflorescent coatings. Its color is emerald-green to apple-green and its streak is pale green.