Štěpite
Chemical formula: U<sup>4+</sup>(As<sup>5+</sup>O<sub>3</sub>OH)<sub>2</sub>·4H<sub>2</sub>O
Štěpite is a very rare, radioactive uranium arsenate, forming characteristic, acicular crystals of an intense yellow-green color.
Description
## Characteristics Štěpite is a hydrated uranyl arsenate, which visually manifests as fine, acicular or hair-like crystals. It typically forms small, radial aggregates, crusts, or tufts of an intense, lemon-yellow to greenish-yellow color. Individual crystals rarely reach sizes visible to the naked eye, so it is most often observed as a micromineral. ## Physical Properties This mineral is very soft, with a hardness of about 2 on the Mohs scale. It exhibits a vitreous luster, and on fibrous aggregates, a silky luster. It is transparent to translucent. Due to the presence of uranium, štěpite is a high-density mineral, approximately 3.66 g/cm³, and also exhibits strong radioactivity. ## Colors and Varieties The color palette of štěpite is limited to shades of yellow and green, most often lemon-yellow, greenish-yellow, and sulfur-yellow. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 2012 by a team of mineralogists led by Jakub Plášil. The name honors the Czech mineralogist and curator of the National Museum in Prague, Josef Štěp (1863–1926), for his contribution to the study of minerals from Jáchymov. The type locality is the Svornost mine in Jáchymov (Czech Republic). ## Applications Due to its extreme rarity, small crystal sizes, and toxicity and radioactivity, štěpite has no industrial applications. It is solely an object of scientific and collecting interest for specialized micromineral collectors.
Diagnostic features
## Identification Characteristic features of štěpite include its habit of fine, acicular crystals forming radial aggregates, intense yellow-green color, and occurrence in paragenesis with other secondary uranium minerals. A key diagnostic feature is strong radioactivity, easily detectable with a Geiger counter. Final confirmation requires advanced analytical methods (e.g., EDS/WDS). ## Differentiation from Similar Minerals Štěpite can be confused with other secondary, acicular uranium minerals of similar color, such as uranophane, cuprosklodowskite, or some minerals from the zippeite group. Uranophane is a silicate and often has a paler yellow color. Differences in chemical composition (presence of arsenic in štěpite) are the basis for their distinction. Visual identification may be impossible without knowledge of the mineral association and analytical confirmation. ## Crystal Forms Crystals are strongly elongated, acicular or hair-like. They almost always occur as radial or stellate aggregates, as well as tangled fibrous masses and crusts on the host rock.
Geological environment
## Genesis Štěpite is a secondary mineral, forming in the oxidation zones of hydrothermal uranium deposits rich in arsenic. It forms as a result of weathering and alteration of primary uranium minerals, mainly uraninite, under the influence of waters rich in dissolved arsenic. ## Mineral Associations This mineral co-occurs with other secondary uranium arsenates, such as metazeunerite, nováčekite, and kahlerite. It is often accompanied by gypsum, and uraninite and other primary sulfides and arsenides are present in the host rock. ## Localities The most important and best-documented occurrence of štěpite in the world is its type locality – the historic Svornost uranium mine in Jáchymov, in the Karlovy Vary region of the Czech Republic. This is the only place from which well-formed, identifiable specimens originate.
Rarity
Very rare
Collector aspects
## Quality Criteria The quality of collector's specimens of štěpite is assessed primarily in the context of micromounting. The most highly valued specimens are those with rich, well-formed, radial aggregates of acicular crystals, deposited on a small fragment of host rock. The intensity and purity of the color and the absence of damage to the delicate needles are important. A contrasting matrix and association with other rare uranium minerals significantly increase the attractiveness of the specimen. ## Popular Localities The only source of valuable collector's specimens is the Svornost mine in Jáchymov, Czech Republic. Specimens from this locality are the standard for this mineral.
Care and storage
## Cleaning Štěpite specimens should generally not be wet cleaned. Any contaminants, such as dust, should be removed only dry, using a soft brush or a photographic air blower. Contact with water can lead to damage of the delicate crystals. ## What to Avoid Štěpite is a highly radioactive (uranium) and toxic (arsenic) mineral. Direct skin contact, inhalation of dust, and ingestion must be strictly avoided. When handling the specimen, it is recommended to wear gloves. The mineral is brittle and sensitive to ultrasound and sudden temperature changes. It should not be exposed to direct sunlight, which can cause its degradation. ## Storage Specimens should be stored in tightly sealed, clearly labeled containers (e.g., "perky box" type) with a warning label about radioactivity and toxicity. Containers should be kept in an area isolated from constant human presence, away from other minerals (to avoid their radiation damage), and out of reach of children and animals.