Formula: Ca_0.5Fe²⁺Fe³⁺₅(PO₄)₄(OH)₆ · 2H₂O

Species: Phosphates

Colour: Dark green, olive-green, olive-brown, black; olive-brown to reddish brown with oxidation; bluish green to reddish brown or yellow in transmitted light.

Lustre: Sub-Vitreous, Resinous, Silky

Hardness: 3½ – 4½

Specific Gravity: 3.1 – 3.34

Crystal System: Monoclinic

Member of: Dufrénite Group. A secondary mineral occurring with limonite in gossan of veins and in iron ore deposits.

Name: Named in 1833 by Alexandre Brongniart in honor of Ours Pierre Armand Petit Dufrenoy (1792-1857), Professor of Mineralogy in the École des Mines, Paris, France. The mineral dufrénoysite is also named in his honor.

Co-Type Localities: Angelard, Compreignac, Bellac, Haute-Vienne, Nouvelle-Aquitaine, France. Hoff auf mich Mine, Ullersreuth, Hirschberg, Saale-Orla District, Thuringia – Germany

Isostructural with: Burangaite, Matioliite, Natrodufrénite