Weeksite

Chemical formula: K₂(U₆+O₂)₂(Si₅O₁₃)·₄H₂O

A radioactive potassium uranyl silicate, forming characteristic, bright yellow aggregates of acicular crystals.

## Characteristics Weeksite is a secondary mineral from the uranyl silicate group, prized by collectors for its intense, lemon-yellow to canary-yellow color. It most often occurs as fine, acicular crystals gathered in radial aggregates, rosettes, or felt-like crusts on the host rock. Less frequently, it forms fibrous or earthy aggregates. Due to the presence of uranium, it is a strongly radioactive mineral. ## Physical Properties Weeksite is very soft, with a Mohs hardness of only 1-2, making it extremely delicate. The luster is most often silky, especially in fibrous aggregates, or dull and earthy in compact aggregates. It is a translucent mineral, and in thin fragments, even transparent. Its density ranges from 3.6 to 3.8 g/cm³. ## Colors and Varieties This mineral does not form color varieties, and its color is constant and characteristic – from light yellow, through lemon, to canary yellow. Sometimes it may take on a slightly brownish hue due to impurities. ## History and Name Weeksite was first described in 1960. Its name honors Mary Dowse Weeks (1904–1999), an American geologist working for the United States Geological Survey (USGS), who made significant contributions to uranium mineralogy research. ## Uses Due to its rarity and small accumulations, weeksite has no industrial application. It is solely an object of scientific interest and a valued collector's stone, especially among collectors of radioactive minerals.

Properties

Mohs hardness: 1-2
Luster: Silky to Earthy
Streak: Pale yellow
Density: 3.6-3.8
Cleavage: Good
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification The most important diagnostic feature of weeksite is its strong radioactivity, easily detected with a Geiger counter. Visually, it is recognized by its bright yellow color and characteristic occurrence in the form of acicular crystals forming radial aggregates or silky crusts. It is very soft and light. ## Distinguishing from Similar Minerals Weeksite is sometimes confused with other yellow secondary uranium minerals. - **Carnotite** is usually more earthy or powdery and has less distinct crystals. - **Uranophane** and **beta-uranophane** form similar aggregates, but their crystals are often more prismatic or bladed, and the hue can be paler, yellowish-green. - **Boltwoodite** also forms radial aggregates, but its crystals are usually brighter and more vitreous. Final differentiation often requires chemical or X-ray diffraction (XRD) analysis, although in collecting practice, crystal form and geological context are key. ## Crystal Forms Weeksite crystals are strongly elongated, acicular. They almost never occur individually. Most often, they form fan-shaped and radial aggregates, spherical aggregates (spherulites), as well as dense, matted masses and crusts with a silky luster.

Geological environment

## Genesis Weeksite is a secondary mineral, formed in the oxidation (weathering) zones of uranium deposits. It forms as a result of low-temperature hydrothermal processes or by the circulation of groundwater, which dissolves and reprecipitates uranium and silica. It most often occurs in porous sedimentary rocks, such as sandstones, conglomerates, or volcanic tuffs. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. Its most common associates include uranophane, boltwoodite, carnotite, as well as opal, chalcedony, calcite, and gypsum. ## Localities The most important and classic weeksite localities are in the USA. The type locality is the area around Thomas Range in Juab County, Utah. Significant specimens also come from the Anderson Mine in Arizona, the Bokan Mountains in Alaska, and numerous occurrences in Nevada and Wyoming. Outside the USA, its presence has been noted in Argentina and Mexico, among others.

Rarity

Rare

For collectors

## Quality Criteria The collector appeal of weeksite depends on several factors. Specimens with well-formed, large (for this mineral) radial aggregates of intense, pure, lemon-yellow color are most highly valued. The contrast with the rock matrix and the presence of associated minerals that create aesthetic compositions are also important. Specimens with minimal mechanical damage are significantly more valuable. ## Popular Localities The localities in the Thomas Range, Utah, USA, are considered classic and yield the best specimens. Many exemplary weeksites found in collections worldwide originate from there. Specimens from the Anderson Mine in Arizona are also prized by collectors.

Care and storage

## Cleaning Weeksite specimens are extremely delicate and sensitive to water. Cleaning should be kept to an absolute minimum. Only very careful dust removal with a soft brush or blowing it away with a stream of compressed air from a safe distance is permissible. Extreme caution should be exercised to avoid inhaling dust. ## What to Avoid Weeksite is strongly radioactive. Direct, prolonged skin contact should be avoided, and above all, inhalation of dust that may arise from careless handling of the specimen. Hands should be thoroughly washed after each contact. The mineral must not be washed with water or any chemical agents. It is very soft, so it should be protected from scratches and impacts. ## Storage Weeksite specimens must be stored in separate, sealed, and clearly labeled containers (e.g., "perky box" type) with information about radioactivity. They should be kept away from areas of permanent human habitation, especially bedrooms and living rooms. It is best to store them in a dedicated collection of radioactive minerals, in a well-ventilated room.