Westerveldite

Chemical formula: FeAs

Westerveldite is a rare iron arsenide, forming metallic, tin-white grains that develop a pinkish-brown tarnish in air.

## Characteristics Westerveldite is an iron arsenide with a metallic appearance. It typically occurs as small, irregular grains or as thin rims around other minerals, primarily niccolite. Fresh surfaces are tin-white with a strong metallic luster, but they quickly dull and develop a characteristic pinkish-brown or brown tarnish upon exposure to air. ## Physical Properties This mineral is opaque and relatively hard, with a Mohs hardness of approximately 5.5. It has a high density, reaching 7.55 g/cm³. It is brittle, and its streak is black. ## Colors and Varieties The primary color of westerveldite is tin-white. On weathered surfaces, the aforementioned tarnish, ranging from pinkish-brown to brown, is observed. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Jan Westerveld (1905–1962), a professor of geology at the University of Amsterdam, who studied ore deposits in the region where the discovery was made. Westerveldite was described as a new mineral in 1972 by I.S. Oen, E.A.J. Burke, and C. Kieft based on samples from the La Gallega mine in Spain. ## Uses Westerveldite has no industrial applications. Its significance is purely scientific and as a collector's item, as a rare component of certain arsenide parageneses.

Properties

Mohs hardness
5.5
Luster
Metallic
Streak
Black
Density
7.55
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification Identifying westerveldite under amateur conditions is very difficult. Clues may include: tin-white color, strong metallic luster, rapid dulling to a pinkish-brown color, high density, and occurrence in association with other nickel, cobalt, and iron arsenides. Definitive identification requires advanced laboratory methods, such as chemical composition analysis (EDS) and X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Westerveldite is almost impossible to distinguish with the naked eye from other metallic arsenides, such as löllingite (FeAs₂), maucherite (Ni₁₁As₈), or rammelsbergite (NiAs₂). Löllingite is usually more silvery-white and more stable. Niccolite (NiAs), with which it often forms intergrowths, has a characteristic copper-pink color. ## Crystal Forms Well-formed westerveldite crystals are extremely rare. This mineral primarily forms anhedral (irregular) grains up to several hundred micrometers in size, often as reaction rims around niccolite grains or as a component of complex multi-mineral aggregates.

Geological environment

## Genesis Westerveldite forms under hydrothermal conditions, typically within serpentinized ultramafic rocks (serpentinites), associated with nickel-copper mineralization. It forms in parageneses with other arsenides and sulfides. ## Mineral Associations This mineral most commonly co-occurs with niccolite, maucherite, löllingite, rammelsbergite, gersdorffite, chalcopyrite, pentlandite, pyrrhotite, and magnetite. ## Localities The most important and type locality is the La Gallega mine in Ojén, Andalusia, Spain. It is also known from the Vammala nickel deposit in Finland, the Ilimaussaq alkaline complex in Greenland, and several occurrences in Canada (Ontario).

Rarity

Rare

For collectors

## Quality Criteria Westerveldite is a mineral valued primarily by systematic collectors and micromounters. The value of a specimen is determined not by its aesthetics, but by the abundance of its occurrence in the sample, confirmed identity (preferably by analysis), and the presence of rare associated minerals. Samples with clearly visible grains or aggregates from the type locality are most desirable. ## Popular Localities The most classic and prized specimens come from the La Gallega mine in Spain. Material for research and collections has also been obtained from Finland (Vammala) and Greenland (Ilimaussaq).

Care and storage

## Cleaning Dry cleaning is recommended, using a soft brush or compressed air to remove dust. Contact with water and any chemical agents, which can accelerate the oxidation process, should be strictly avoided. ## What to Avoid The mineral is sensitive to moisture and atmosphere, which cause it to dull and change color. Avoid contact with acids and other chemicals. Due to its arsenic content, when mechanically processing (cutting, grinding), avoid inhaling dust. ## Storage Westerveldite specimens are best stored in dry and stable conditions. Airtight containers or display cases with a desiccant are recommended to limit oxidation processes and preserve the mineral's natural luster.

External references

Sources

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