Whitecapsite

Chemical formula: H₁₆Fe₂+₅Fe₃+₁₄Sb₃+₆(As₅+O₄)₁₈O₁₆·₁₂₀H₂O

Whitecapsite is an extremely rare, hydrated iron and antimony arsenate, forming microscopic, yellow crystalline aggregates.

## Characteristics Whitecapsite is a secondary mineral from the arsenate group, with a very complex chemical composition. It occurs as microscopic, acicular or hair-like crystals, which most often form radial, spherulitic aggregates or delicate crusts and coatings. Individual crystals rarely exceed 1 mm in length. Due to its size, it is a typical micromount mineral, impossible to identify without specialized equipment. ## Physical properties This mineral is very brittle. Its Mohs hardness is about 2, and its density calculated from the chemical formula is 2.81 g/cm³. The crystals exhibit a vitreous luster, transitioning to silky in the case of fine-fibrous aggregates. They are transparent to translucent. ## Colors and varieties Whitecapsite has a characteristic, bright color, from canary yellow to yellowish-brown. The streak is light yellow. No varieties have been distinguished. ## History and name The mineral was approved by the International Mineralogical Association (IMA) in 2012. Its name comes from the discovery locality – the White Caps gold mine in the Manhattan district, Nye County, Nevada (USA). This is the only known occurrence of this mineral in the world. ## Applications Whitecapsite has no practical application. It is solely an object of scientific research and a valuable acquisition for specialized micromount mineral collectors.

Properties

Mohs hardness: 2
Luster: Vitreous to silky
Streak: Pale yellow
Density: 2.81
Cleavage: None
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Amateur identification of whitecapsite is impossible. Its physical characteristics, such as color and habit, are similar to many other secondary arsenic minerals. Positive identification requires advanced analytical techniques, such as X-ray diffraction (XRD) to determine the crystal structure and chemical analysis (e.g., EDS/WDS) to confirm its unique, complex composition. ## Distinguishing from similar minerals Whitecapsite can be easily confused with other yellow, secondary arsenates found in the same environment, such as pharmacosiderite, scorodite, pitticite, or yukonite. It is distinguished from most of them by the presence of antimony in its composition, which can only be determined by laboratory methods. ## Crystal forms It forms very small, acicular or hair-like crystals with a hexagonal cross-section. These crystals almost always occur in the form of radial or tangled aggregates, as well as spherical spherulites and thin coatings on the host rock.

Geological environment

## Genesis Whitecapsite is a secondary (supergene) mineral, formed in the oxidation (weathering) zone of polymetallic deposits rich in arsenic and antimony. It forms under post-mining conditions, crystallizing on the walls of old mine workings as a result of the interaction of sulfate-rich solutions with primary minerals. ## Mineral associations This mineral occurs in association with other rare, secondary arsenates and sulfates. The most common associated minerals at the type locality include: pitticite, yukonite, pharmacosiderite, scorodite, jarosite, gypsum, and goethite. ## Localities The only confirmed and described occurrence of whitecapsite in the world is its type locality: the White Caps mine, near Manhattan, Nye County, Nevada, USA.

Rarity

Extremely rare

For collectors

## Quality criteria For micromount mineral collectors, the most important criteria for evaluating a whitecapsite specimen are: the richness and abundance of aggregates on the host rock, the intensity and purity of the yellow color, and the aesthetic composition with other associated minerals. Specimens with well-formed, radial aggregates are highly prized. ## Popular localities As this mineral is known from only one locality in the world, all collectible specimens come from the White Caps mine in Nevada. This is a classic locality for many rare, secondary arsenic minerals.

Care and storage

## Cleaning Whitecapsite specimens are extremely delicate and sensitive. The only safe method for dust removal is using compressed air from a safe distance. Any contact with water, chemical solutions, or mechanical cleaning (e.g., brushes) should be avoided. ## What to avoid As a hydrated mineral, it is sensitive to high temperatures, which can lead to dehydration and destruction of its structure. It should be protected from direct sunlight, which can cause fading. It is chemically reactive and is destroyed upon contact with acids and other chemicals. Due to its arsenic content, dust inhalation should be avoided, and hands should be washed after contact with the specimen. ## Storage It is recommended to store specimens only in sealed "micromount" boxes, which protect them from mechanical damage, dust, and humidity fluctuations. They should be kept in stable conditions, away from heat and light sources.

Sources

IMA Mineral List (CNMNC)