Goldichite

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

Goldichite is a rare, hydrated potassium iron sulfate, forming characteristic acicular crystals with a vitreous luster.

## Characteristics Goldichite is a mineral from the sulfate group, chemically a hydrated potassium iron sulfate. It is rare, forming aggregates of small, prismatic or acicular crystals that can reach up to 2 cm in length. It often forms radial aggregates, rosettes, or crusts. Its crystals are typically elongated and well-formed. ## Physical Properties This mineral is characterized by relatively low hardness, measuring 2.5 on the Mohs scale, which means it is quite soft and susceptible to scratching. It has a vitreous luster. It is a brittle mineral, with a density of 2.43 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Goldichite occurs in various shades, from colorless, through white, pale yellow, to greenish-yellow. Its color depends on impurities and crystallization conditions. No named varieties of this mineral are distinguished. ## History and Name The mineral is named in honor of Frank Goldich (1878-1964), an American geochemist and petrologist, professor at the University of Minnesota and an employee of the United States Geological Survey (USGS). The mineral was first described in 1955 based on samples from the Dexter No. 7 mine in Calf Mesa, San Rafael Swell, Utah, USA. ## Uses Due to its rarity and small crystal size, goldichite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientists.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
Pale yellow
Density
2.43
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Goldichite can be identified by its characteristic crystal habit – typically small, acicular or prismatic crystals gathered in radial aggregates. Key features include its low hardness, vitreous luster, and color, most often in shades of yellow. Its water solubility is crucial. ## Distinguishing from Similar Minerals It can be confused with other secondary iron sulfates, such as jarosite or metavoltine. Differentiation often requires chemical analysis (XRD, EDS), as visual characteristics can be very similar. However, jarosite is harder (2.5-3.5) and crystallizes in the trigonal system, while goldichite crystallizes in the monoclinic system. ## Crystal Forms Goldichite crystals are typically acicular or prismatic, elongated along one axis. They form fibrous, radial, rosette-like aggregates, as well as thin crusts and coatings on the host rock.

Geological environment

## Genesis Goldichite is a secondary mineral, forming in the oxidation (weathering) zones of sulfide deposits, especially those containing pyrite or marcasite. It forms under arid and desert conditions as a product of evaporation of sulfate-rich solutions. It results from the reaction of percolating waters with iron and sulfur minerals. ## Mineral Associations It often co-occurs with other secondary sulfates, such as gypsum, melanterite, copiapite, jarosite, metavoltine, and native sulfur. ## Localities The most important and classic locality (type locality) is the Dexter No. 7 mine in Calf Mesa, San Rafael Swell, Utah, USA. This mineral has also been found in other arid regions, including a mine in the Tierra Amarilla area in Chile and the Freedom No. 2 mine in Montrose County, Colorado, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, distinct crystals forming aesthetic, radial aggregates or rosettes. The intensity and purity of color (yellow and greenish-yellow shades are preferred) and contrast with the rock matrix are important. Due to the mineral's rarity, even small but well-formed crystalline aggregates are considered valuable. ## Popular Localities Specimens from the type locality in Utah, USA, are by far the most sought after, considered classic and best for this mineral.

Care and storage

## Cleaning Goldichite specimens are very delicate and water-soluble. Wet cleaning should be avoided. Only careful dust removal using a soft brush or a stream of compressed air from a safe distance is permissible. ## What to Avoid Contact with water, acids, and other chemicals that can damage or dissolve it must be strictly avoided. The mineral is brittle, so it must be protected from impacts and vibrations. It should not be heated or exposed to humid air. ## Storage Goldichite specimens are best stored in closed, airtight containers (e.g., "membrane box" or a box with cotton batting) that protect against moisture, dust, and mechanical damage. It is advisable to add a desiccant, such as silica gel, to the container.

Sources

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