Hubbardite

Chemical formula: Mg(H<sub>2</sub>O)<sub>6</sub>[(U<sup>6+</sup>O<sub>2</sub>)<sub>2</sub>O(OH)(S<sup>6+</sup>O<sub>4</sub>)]<sub>2</sub>·8H<sub>2</sub>O

Hubbardite is a very rare, hydrated uranyl magnesium sulfate, forming microscopic, yellow crystals with a vitreous luster.

## Characteristics Hubbardite is a secondary mineral from the uranyl sulfate group, occurring as extremely small, platy or acicular crystals that rarely exceed 0.2 mm in length. It forms radial aggregates and crusts of an intensely yellow color. Due to the microscopic size of the crystals, its visual features are difficult to observe without specialized equipment. ## Physical Properties Hubbardite crystals exhibit a vitreous luster. They are brittle, and their hardness and density have not been precisely measured due to the small size of the samples. The mineral is transparent to translucent. ## Colors and Varieties Hubbardite occurs in a uniform, pale yellow color. No varieties have been distinguished. ## History and Name The mineral was named in honor of Richard "Rick" C. Hubbard (born 1947), an American mineral collector from New Mexico, who provided the first samples for study. It was approved as a new mineral species by the International Mineralogical Association (IMA) in 2018 (IMA2018-031). The type locality is the Giveway-Simplot uranium mine in the White Canyon district, San Juan County, Utah, USA. ## Uses Hubbardite, as a uranium-bearing mineral, is radioactive. It has no industrial application and is of purely scientific and collecting interest for specialized collectors of uranium minerals.

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light yellow
Density
3.11
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of hubbardite is based on its characteristic form – tiny, acicular or platy crystals forming radial aggregates of a pale yellow color. The location (uranium mines in Utah) and co-occurrence with other uranyl sulfates are crucial. The mineral exhibits strong, green fluorescence under shortwave UV light. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or spectroscopy. ## Distinguishing from Similar Minerals Hubbardite can be confused with many other yellow secondary uranium minerals, such as zippeite, uranophane, or meta-autunite. Distinguishing it with the naked eye is practically impossible. It differs from them in subtle color shades, crystal habit (visible under high magnification), and chemical and structural properties, which can only be examined in a laboratory. ## Crystal Forms Crystals are very small, acicular or platy, elongated along the [100] axis and flattened on {010}. They typically form radial or stellate aggregates and thin crusts on the host rock.

Geological environment

## Genesis Hubbardite is a secondary mineral that forms in the oxidation zone of uranium deposits. It crystallizes as a result of the activity of sulfate-rich waters interacting with primary uranium ores (uraninite) in the presence of magnesium. It forms in voids and on fracture surfaces in sedimentary rocks, mainly sandstones. ## Mineral Associations This mineral co-occurs with other secondary uranyl sulfates and silicates. It is most commonly associated with gypsum, hexahydrite, epsomite, bobcookite, wetherillite, zippeite, and uranophane. ## Localities The only confirmed locality for hubbardite in the world is its type locality – the Giveway-Simplot mine in the White Canyon district, San Juan County, Utah, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria The collecting appeal of hubbardite depends on the richness and aesthetics of the crystal aggregates on the rock matrix. The most prized specimens are those with well-formed, radial clusters of an intense, pale yellow color that clearly contrast with the darker sandstone background. Due to the microscopic nature of the crystals, their photogenicity under magnification is crucial. ## Popular Localities The only source of hubbardite specimens is the Giveway-Simplot mine in Utah, USA. Material from this locality is extremely rare and sought after by specialized collectors of uranium minerals and "micromounts."

Care and storage

## Cleaning Hubbardite specimens should generally not be cleaned. Any attempts at mechanical or chemical cleaning can irreversibly damage the delicate, microscopic crystals. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust particles. ## What to Avoid Contact with water, which can dissolve the mineral, must be strictly avoided. It should be protected from all chemicals, ultrasound, and high temperatures. As a uranium mineral, it is radioactive, so direct exposure should be limited, and hands should always be washed after handling a specimen. ## Storage Hubbardite specimens should be stored in closed, airtight containers (such as "micromount boxes") to protect them from mechanical damage, dust, and humidity changes. Due to its radioactivity, it should be stored away from areas of permanent human habitation, in an appropriately marked location.

Sources

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