Sharpite

Chemical formula: Ca(U<sup>6+</sup>O<sub>2</sub>)<sub>3</sub>(CO<sub>3</sub>)<sub>4</sub>·3H<sub>2</sub>O

Sharpite is a rare, secondary uranyl mineral, forming bright yellow, acicular crystals and coatings on uraninite.

## Characteristics Sharpite is a hydrated calcium uranyl carbonate, occurring in the oxidation zones of uranium deposits. It forms characteristic, fine, acicular or fibrous crystals, which often arrange themselves into radial aggregates, rosettes, or form delicate, felt-like coatings. Individual crystals are usually microscopic in size, and their clusters rarely exceed a few millimeters. ## Physical Properties Sharpite crystals exhibit a silky or vitreous luster. Due to its microcrystalline and fibrous nature, it is a very brittle mineral. It is highly radioactive due to its high uranium content. ## Colors and Varieties Sharpite has a characteristic bright yellow, canary yellow, or greenish-yellow color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described by the Belgian mineralogist Johannes Fromme in 1926. The name honors Dr. Robert R. Sharp (1881–1958), a professor of radiology at the University of Brussels, who studied uranium deposits in Shinkolobwe. ## Uses Sharpite has no industrial application. It is of purely scientific and collectible interest as a rare secondary uranium mineral.

Properties

Luster
Silky
Streak
Pale yellow
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Sharpite is identified by its characteristic bright yellow color, acicular or fibrous crystal form, and radial aggregates. Its occurrence in paragenesis with other secondary uranium minerals on uraninite is key. It exhibits strong green fluorescence under ultraviolet light (both short-wave and long-wave). ## Distinguishing from Similar Minerals Sharpite is visually very similar to other acicular uranyl minerals, such as studtite, metaschoepite, or rutherfordine. Certain distinction often requires advanced analytical methods, such as X-ray diffraction (XRD). It can be preliminarily distinguished based on paragenesis – sharpite often co-occurs with becquerelite and curite. ## Crystal Forms The mineral forms very fine, elongated, acicular or bladed crystals, which almost always occur as radial or spherulitic aggregates. It also forms compact, felt-like or earthy coatings and crusts.

Geological environment

## Genesis Sharpite is a secondary mineral, formed in the oxidation (weathering) zone of hydrothermal uranium deposits. It forms as a result of the interaction of carbonate-rich waters with primary uranium minerals, mainly uraninite. It is one of the later products of this process. ## Mineral Associations It most commonly co-occurs with uraninite (as a primary mineral) and other secondary uranium minerals, such as becquerelite, curite, schoepite, rutherfordine, fourmarierite, masuyite, and ianthinite. ## Localities The most important and classic locality for sharpite is the Shinkolobwe mine in Upper Katanga Province, Democratic Republic of Congo, from which the best known specimens originate. It has also been found in small quantities in the Menzenschwand mine in the Black Forest (Germany) and in the Lake Athabasca region in Saskatchewan (Canada).

Rarity

Very rare

For collectors

## Quality Criteria The most prized sharpite specimens are those with well-formed, radial aggregates of intense, canary-yellow color, contrasting with a dark uraninite matrix. The absence of damage to the delicate needles and a rich paragenesis with other rare uranyl minerals from the same locality are important. ## Popular Localities By far the most sought-after and valuable specimens come from the historical type locality – the Shinkolobwe mine in the DRC. Specimens from other locations are rare on the collector's market and are mainly of scientific interest.

Care and storage

## Cleaning Sharpite specimens are generally not cleaned. Any attempts at mechanical cleaning (brushes) or chemical cleaning (water, solvents) can irreversibly damage the delicate crystals. Only very careful removal of loose contaminants using a photographic blower (non-contact) is permissible. ## What to Avoid Avoid contact with water and chemicals, which can dissolve the mineral. The crystals are extremely brittle and sensitive to touch, vibrations, and temperature changes. As a uranium mineral, it is highly radioactive and requires special precautions – avoid inhaling dust and direct skin contact. ## Storage Specimens should be stored in sealed, lockable containers (e.g., "perky box" type) to protect them from mechanical damage, dust, and moisture. Due to radioactivity, it should be stored away from areas of permanent human habitation, in a designated place, preferably in a lead container, if the collection contains larger or numerous specimens.

Sources

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