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Johannit - Ronneburg.jpg
Category Sulfate mineral
(repeating unit)
Strunz classification 7.EB.05 (10 ed)
VI/D.21-10 (8 ed)
Dana classification
Crystal system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
Space group P1
Color Emerald-green, apple-green
Twinning Simple and repeated lamellar twinning
Cleavage good on {100}
Mohs scale hardness 2 - 2.5
Luster Vitreous
Streak Pale green
Diaphaneity Transparent, Translucent
Density 3.32
Optical properties Biaxial (+/-)
Refractive index 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 angle 90°
References [1][2][3]

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.

Johannite is a strong radioactive mineral with a calculated activity of 87,501,143 Bq/g (to the comparison: natural potassium: 31.2 Bq/g).

Etymology and history[edit]

Johannite was first described in 1830 by Wilhelm Karl Ritter von Haidinger. It was named for Archduke John of Austria (1782–1859), the founder of the Landesmuseum Joanneum (Styria, Austria).


Johannite forms as secondary mineral by oxidation from uraninite as well as different other uranium minerals

Localities include Argentina, Czech Republic, France, Gabon, Germany, Greece, Italy, Switzerland, United Kingdom and the United States. Type locality is the “Elias Mine” in Jáchymov (Czech Republic).

Crystal structure[edit]

Johannite crystallizes in the triclinic crystal system in the space group P1 with the lattice parameters a = 8.92 Å, b = 9.59 Å, c = 6.84 Å; α = 110°, β = 111.98°, γ = 100.3° and one formula unit per unit cell.