Butlerite

Chemical formula: Fe<sup>3+</sup>S<sup>6+</sup>O<sub>4</sub>(OH)·2H<sub>2</sub>O

Butlerite is a rare, orange iron sulfate, forming fine, acicular crystals in the oxidation zones of ore deposits.

## Characteristics Butlerite is a hydrated iron sulfate, typically occurring as delicate, fibrous or acicular crystals of small size. It forms radial aggregates, crusts, or coatings. Due to its fragility and small crystal size, specimens are usually admired in the form in which they grew on the host rock (matrix). ## Physical Properties Butlerite crystals are very soft, with a hardness of 2-2.5 on the Mohs scale, meaning they can be scratched with a fingernail. They have a vitreous luster, transitioning to silky in the case of fibrous aggregates. They are transparent to translucent. The mineral's density is approximately 2.54 g/cm³. ## Colors and Varieties This mineral is characterized by an intense, orange to yellowish-orange color. No color or commercial varieties are distinguished. ## History and Name Butlerite was first described in 1928 by Carl Lausen from specimens found in the United Verde mine in Jerome, Arizona (USA). The mineral is named in honor of Gurdon Montague Butler (1881–1961), an American geologist and dean of the College of Mines and Engineering at the University of Arizona. ## Uses Butlerite has no industrial application. It is solely a mineral of scientific and collector's interest, sought after for its rarity and attractive color.

Properties

Mohs hardness
2-2.5
Luster
Vitreous
Streak
Pale yellow
Density
2.54
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Butlerite is identified by its characteristic orange color, fibrous or acicular crystal habit, and occurrence in the oxidation zones of sulfide deposits. A key feature is its reaction to moisture – it is water-soluble. ## Distinguishing from Similar Minerals It can be confused with other secondary iron sulfates, such as copiapite or paracoquimbite. Copiapite usually has a more yellow or greenish-yellow hue. Paracoquimbite, although similar, crystallizes in the trigonal system and has slightly different properties. Definitive differentiation often requires chemical (EDS) or X-ray (XRD) analysis. ## Crystal Forms Butlerite forms very small, prismatic or acicular crystals, often elongated and striated along the main axis. They most commonly occur as radial aggregates, rosettes, crusts, or as microcrystalline coatings.

Geological environment

## Genesis Butlerite is a secondary mineral, formed by the weathering (oxidation) of sulfide minerals, mainly pyrite, in dry and hot climatic conditions. It forms as a product of mine fires or mining dumps (fumaroles). ## Mineral Associations It often co-occurs with other secondary sulfates, such as copiapite, paracoquimbite, coquimbite, voltaite, jarosite, as well as gypsum and native sulfur. ## Localities Important localities worldwide include the United Verde mine in Jerome, Arizona (type locality); Calama in Chile; Vulcano Island in Italy; Rammelsberg mine in Germany; and La Alcaparrosa mine in Spain.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, distinct crystals of intense orange color, forming aesthetic, radial aggregates on a contrasting rock matrix. Due to the small size of the crystals, specimens are primarily evaluated under a microscope, and their value increases with the richness and aesthetics of the aggregates. ## Popular Localities Specimens from the type locality (United Verde mine, Arizona) have historical value. High-quality microcrystals also come from the Rammelsberg mine in Germany and from fumaroles on Vulcano Island in Italy.

Care and storage

## Cleaning Butlerite is very sensitive to water and moisture. It must absolutely not be cleaned wet. The only safe method is gentle dust removal using a soft brush or a photographic air blower. ## What to Avoid Avoid all contact with water, water vapor, and high humidity, which can cause the mineral to dissolve or chemically alter. It should also be protected from chemicals, ultrasound, and sudden temperature changes. ## Storage Butlerite specimens must be stored in dry conditions. It is best to keep them in sealed, enclosed boxes (e.g., "perky boxes") or in display cases with a moisture absorber (e.g., silica gel).

Sources

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