Fermiite

Chemical formula: Na₄(U⁶⁺O₂)(S⁶⁺O₄)₃·₃H₂O

Fermiite is a very rare, water-soluble uranyl mineral, forming microscopic, yellow crystals and coatings.

## Characteristics Fermiite is a secondary uranyl sulfate that forms as coatings and aggregates of small, acicular or bladed crystals. Individual crystals are very small, usually not exceeding 0.2 mm in length, and often form radial aggregates or thin crusts on the surface of the host rock. Due to its chemical composition, this mineral is strongly radioactive. ## Physical Properties Fermiite crystals exhibit a bright yellow color and a vitreous luster. They are transparent to translucent. The mineral is soft and brittle. One of its key and unusual features is its solubility in water at room temperature, which requires special care when handling specimens. ## History and Name Fermiite was first described in 2014 by a team of mineralogists led by Jakub Plášil. The mineral is named in honor of Enrico Fermi (1901–1954), an Italian-American physicist, Nobel laureate, who built the world's first nuclear reactor, Chicago Pile-1, and made fundamental contributions to the development of nuclear physics. The approval of the new mineral by the International Mineralogical Association (IMA) occurred in the same year (IMA2014-0 Fermiite).

Properties

Mohs hardness: 2.5
Color: Pale greenish-yellow
Luster: Vitreous
Streak: White
Density: 3.23
Cleavage: no cleavage
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Orthorhombic

Diagnostic features

## Identification A key diagnostic feature of fermiite is its water solubility. In field and collecting conditions, it is recognized by its bright yellow color, the form of small, acicular crystals forming coatings, and strong radioactivity. The mineral also exhibits characteristic greenish-yellow fluorescence under shortwave ultraviolet (UV-SW) light. ## Distinguishing from similar minerals Fermiite can be confused with many other yellow secondary uranium minerals, such as zippeite, uranophane, or metaautunite. Distinguishing it without specialized testing is difficult. The water solubility test is helpful but destructive to the sample. Only chemical analysis (EDS) or X-ray diffraction (XRD) allows for certain identification. ## Crystal forms Fermiite crystallizes in the form of very small, elongated crystals with an acicular or bladed habit. These crystals often combine into radial or stellate aggregates, and also form thin, dusty coatings and crusts on rock surfaces.

Geological environment

## Genesis Fermiite is a secondary mineral, formed as a result of weathering (oxidation) of primary uranium ores, mainly uraninite, in a sulfate-rich environment. It forms as an evaporation product of mine waters in dry conditions, crystallizing on the walls of mine workings. ## Mineral associations This mineral occurs in association with other secondary sulfates and uranyl sulfates. In its type locality (Blue Lizard mine), it was found in association with gypsum, hexahydrite, as well as minerals from the zippeite group, johannite, uranopilite, and wölsendorfite. ## Localities The only confirmed occurrence of fermiite in the world is its type locality – the Blue Lizard mine in San Juan County, Utah, USA. This is an area rich in uranium and vanadium deposits, known for the occurrence of many rare secondary minerals.

Rarity

Very rare

For collectors

## Quality criteria The collector's appeal of fermiite primarily depends on the richness and aesthetics of the coating on the host rock. The most prized specimens are those with clearly visible, abundant aggregates of small, acicular crystals that form an intensely yellow covering. Contrast with the dark host rock also enhances visual value. Due to the microscopic size of the crystals, their individual form is less important than the overall appearance of the aggregate. ## Popular localities The only source of fermiite specimens is the Blue Lizard mine in Utah, USA. All samples available on the collector's market come from this single location.

Care and storage

## Cleaning The mineral must absolutely not be wet-cleaned, as it is water-soluble. Specimens can only be cleaned mechanically, using a very soft brush or carefully blowing off dust with compressed air from a safe distance. ## What to avoid Avoid all contact with water and other liquids, which can instantly damage or destroy the specimen. The mineral is sensitive to moisture, so it should be protected from high humidity. As a uranium mineral, it is strongly radioactive – it requires safe handling, avoiding dust inhalation, and washing hands after each contact. ## Storage Fermiite specimens must be stored in dry conditions, preferably in sealed, airtight containers (so-called "perky boxes") with a desiccant (e.g., silica gel). Due to radioactivity, they should be kept away from other radiation-sensitive minerals, out of reach of children and pets, and appropriately labeled.