Gunterite

Chemical formula: Na₄Ca[V⁵⁺₁₀O₂₈]·20H₂O

Gunterite is a very rare, hydrated sodium and calcium vanadate, forming microscopic, orange-yellow crystals with low hardness.

## Characteristics Gunterite is a mineral from the pascoite group, belonging to the vanadate class. It occurs as very small, bladed or acicular crystals, rarely exceeding 1 mm in length. It forms radial aggregates, rosettes, and crusts. Its characteristic feature is an intense, orange-yellow color. ## Physical Properties This mineral is extremely soft, with a hardness of only 1 on the Mohs scale, meaning it can be scratched with a fingernail. It is brittle, and its density calculated from the formula is approximately 2.4 g/cm³. The crystals exhibit a luster described as vitreous to pearly. Depending on the thickness of the crystals, it is transparent to translucent. ## Colors and Varieties Gunterite occurs in a uniform, orange-yellow color. No color or commercial varieties have been distinguished. ## History and Name The mineral's name honors Mickey and Brenda Gunter of Ouray, Colorado (USA), in recognition of their contributions to the mineralogy of the region. Gunterite was approved as a new mineral species by the International Mineralogical Association (IMA) in 2022. It was discovered at the West Sunday Mine in the Slick Rock mining district, Colorado. ## Uses Due to its extreme rarity, small crystal size, and low hardness, gunterite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals (so-called micromounts).

Properties

Mohs hardness
1
Luster
Vitreous, Pearly
Streak
Yellow
Density
2.398
Fracture
Irregular/Uneven
Transparency
Transparent, Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of gunterite include its orange-yellow color, occurrence as small, acicular or bladed crystals forming radial aggregates, and extremely low hardness (1 on the Mohs scale). Its origin is also key – it occurs in sedimentary rocks (sandstones) rich in uranium and vanadium. ## Distinguishing from Similar Minerals It can be confused with other secondary vanadium minerals, such as pascoite, lasalite, or huemulite, which often co-occur and have similar colors. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS), due to visual similarity and co-occurrence. ## Crystal Forms Gunterite forms elongated, bladed or acicular crystals that combine into radial, star-shaped aggregates and rosettes. It also occurs as thin crusts on the surface of the host rock.

Geological environment

## Genesis Gunterite is a secondary vanadium mineral that forms in the oxidation zone of uranium-vanadium deposits located in sedimentary rocks, mainly sandstones. It forms as a result of the weathering of primary ore minerals in arid conditions, within pores and fractures of the host rock. ## Mineral Associations This mineral occurs in association with other rare, secondary vanadates. It most commonly co-occurs with pascoite, huemulite, lasalite, as well as gypsum and montmorillonite. ## Localities The only confirmed locality for gunterite worldwide is its type locality – the West Sunday Mine in the Slick Rock mining district, San Miguel County, Colorado, USA.

Rarity

Extremely rare

For collectors

## Quality Criteria For gunterite collectors, the size and quality of crystal aggregate formation are most important. Specimens with distinct, radial rosettes of intense, orange-yellow color, well-contrasted against the host rock, are most prized. Due to the microscopic nature of the mineral, the aesthetics of the entire aggregate, rather than individual crystals, are crucial. ## Popular Localities The only known source of gunterite specimens is the West Sunday Mine in Colorado, USA. All specimens available on the collector's market originate from this single locality.

Care and storage

## Cleaning Gunterite specimens are extremely delicate and sensitive to water. They should not be wet cleaned. To remove dust, a very soft brush or a photographic air blower can be used very carefully, avoiding direct contact with the crystals. ## What to Avoid Contact with water, chemicals, soap, and ultrasonics must be absolutely avoided. The mineral is water-soluble. Its low hardness (1 on the Mohs scale) makes it susceptible to the slightest scratches and mechanical damage. It should be protected from changes in humidity and temperature. ## Storage Gunterite specimens should be stored under stable conditions, preferably in sealed, closed "micromount" boxes that protect them from dust, moisture, and physical damage. Avoid exposure to direct sunlight.

External references

Sources

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