Formula: Fe3+(SO4)(OH).2H2O
Hydrated sulphate containing hydroxyl, monoclinic paramorph of parabutlerite, which is orthorhombic. Butlerite is sometimes epitaxial on parabutlerite.
Specific gravity: 2.548
Hardness: 2½
Streak: Pale yellow
Colour: Dark orange, light yellow-orange in transmitted light.

Hydrothermal environments
Mine fires

Butlerite is rarely formed from the oxidation of pyritic ore and it may be formed under fumarolic conditions in mine fires. Associated minerals include parabutlerite, copiapite, fibroferrite and other iron sulfates (HOM).


At the Santa Elena Mine, Quebrada Alcaparrosa, Calingasta, Calingasta Department, San Juan Province, Argentina, butlerite occurs as oriented intergrowths with parabutlerite (AM 27.144).

The type locality, the United Verde Mine, Black Hills, Yavapai county, Arizona, USA, hosts six type minerals that formed as the result of a mine fire that started in 1894 and burned for decades (R&M 87.1.10 ). Butlerite was formed by the oxidation of pyrite in the fire with reactions with water, steam and carbon dioxide used for fire fighting. It is associated with copiapite (Mindat, Dana).

At the Dexter group, Calf Mesa, San Rafael Mining District, Emery county, Utah, USA, the paramorphs butlerite and parabutlerite occur as encrustations of small crystals with copiapite or melanterite (AM 40.478).

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