Gatewayite

Chemical formula: Ca₆(As₃+V₄+₃V₅+₉As₅+₆O₅₁)·₃₁H₂O

Gatewayite is an extremely rare, hydrated calcium arsenate-vanadate, forming microscopic, dark red crystalline aggregates.

## Characteristics Gatewayite is a mineral with a very complex chemical composition, belonging to the group of hydrated arsenates and vanadates. It occurs as microscopic aggregates, rarely exceeding 0.2 mm in diameter. It forms spherical clusters or rosettes composed of extremely thin, platy crystals less than one micrometer thick. Its color is dark reddish-brown, sometimes almost black, which, combined with its small size, makes it difficult to observe with the naked eye. ## Physical properties The mineral exhibits a vitreous to subadamantine luster. It is translucent. Due to its extreme brittleness and small crystal size, its Mohs hardness has not been determined. The density calculated from unit cell parameters is 2.82 g/cm³. ## Colors and varieties Gatewayite occurs in a uniform, dark reddish-brown to almost black color. No color varieties or commercial names are known. ## History and name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2022 (IMA2022-031). Its name comes from the town of Gateway, Colorado (USA), located near the discovery site. Gatewayite was first identified in the Blue Cap mine in San Juan County, Utah, USA. The scientific description of the mineral was published in 2023 in the "Mineralogical Magazine" by a team led by Anthony R. Kampf. ## Applications As a microscopic and extremely rare mineral, gatewayite has no industrial applications. It is solely an object of scientific research and a valuable acquisition for specialized collectors of rare minerals (so-called micromounters).

Properties

Luster: Vitreous to sub-adamantine
Streak: Light brown
Density: 2.82
Cleavage: Perfect on {010}
Transparency: Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Amateur identification of gatewayite is impossible. Due to its microscopic size and occurrence in association with other visually similar minerals, its definitive identification requires advanced analytical techniques such as X-ray diffraction (XRD) and chemical microanalysis (EDS). Visual features that may suggest its presence are characteristic spherical aggregates of platy crystals with a dark red color. ## Distinguishing from similar minerals Gatewayite can be confused with other secondary, reddish-brown vanadium minerals found in the same locality, such as huemulite, pascoite, or lasalite. Final differentiation is only possible based on structural and chemical analysis, as their physical properties and appearance can be very similar. ## Crystal forms Gatewayite crystals have the form of extremely thin plates. They combine into spherical aggregates and rosettes, which are the typical form of occurrence for this mineral.

Geological environment

## Genesis Gatewayite is a secondary mineral that forms in the oxidation zone of uranium-vanadium deposits embedded in sandstones. It forms contemporaneously (it is a post-mining mineral) on rock surfaces and mine workings walls as a result of weathering processes of primary ore minerals in an arid climate. ## Mineral associations This mineral co-occurs with a number of other rare, secondary vanadates. Its most common associations include: bluecapite, anselmite, huemulite, lasalite, pascoite, rossite, raberite, and sherwoodite. ## Localities The only confirmed locality of gatewayite in the world is its type locality – the Blue Cap mine, in the La Sal district, San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality criteria For micromineral collectors, the most important criteria for evaluating a gatewayite specimen are: the development and aesthetics of the aggregates (well-formed, spherical rosettes are preferred), the abundance of the mineral on the rock matrix, and the presence of interesting associated minerals. The size of the aggregates, although always microscopic, is also important – larger clusters (reaching 0.2 mm) are more highly valued. ## Popular localities Gatewayite specimens come exclusively from one location in the world – the Blue Cap mine in Utah, USA. This is the only source for obtaining this mineral for collections and scientific institutions.

Care and storage

## Cleaning Gatewayite specimens are extremely delicate and susceptible to mechanical damage. They should absolutely not be cleaned with brushes, ultrasound, or any liquids. The only permissible method for dust removal is very careful use of a photographic blower or other non-contact source of a gentle air stream. ## What to avoid The mineral is sensitive to humidity changes due to the high water content in its crystal structure – it can dehydrate. Contact with all chemicals, including water, should be avoided. It should be protected from temperature fluctuations, direct sunlight, and vibrations. ## Storage Gatewayite must be stored in a specialized, tightly sealed "micromount" box. This provides protection against physical damage, dust, and stabilizes ambient humidity, minimizing the risk of crystal degradation.

Sources

IMA Mineral List (CNMNC)