Formula: Cu(UO₂)₂(SO₄)₂(OH)₂ · 8H₂O

Species: Sulfates

Colour: Emerald-green, apple-green

Lustre: Vitreous

Hardness: 2 – 2½

Specific Gravity: 3.32

Crystal System: Triclinic

Name: After Archduke Johann (1782-1859) of Austria, founder of the Styrian Landesmuseum, Graz.

Type Locality: Elias Mine, Jáchymov, Karlovy Vary District, Karlovy Vary Region – Czech Republic