Sabugalite

Chemical formula: HAl(U₆+O₂)₄(PO₄)₄·₁₆H₂O

Sabugalite is an intensely yellow, secondary uranium mineral, forming characteristic thin, square crystals and coatings on rocks.

## Characteristics Sabugalite is a mineral belonging to the autunite group, known for its bright, lemon-yellow to greenish-yellow color. It occurs in the oxidation zones of uranium deposits. It typically forms thin, tabular crystals with a square outline, which often arrange into rosette-like aggregates, fans, or form thin coatings and efflorescences on the surface of host rocks, mainly granites and pegmatites. Due to its uranium content, it is a highly radioactive mineral and exhibits intense, greenish-yellow fluorescence under ultraviolet light (both shortwave and longwave). ## Physical Properties Sabugalite crystals are very soft and brittle, with a hardness of about 2.5 on the Mohs scale. They have a luster described as waxy, dull, or earthy, and can be pearly on cleavage surfaces. It is a light mineral, with a density of about 3.2 g/cm³. Crystals are usually translucent to opaque. ## Colors and Varieties This mineral is monochromatic – it occurs in shades from pale yellow, through lemon-yellow, to greenish-yellow. No color varieties or commercial varieties are distinguished. ## History and Name Sabugalite was first described in 1951 by Clifford Frondel. Its name comes from its discovery locality – the Mina da Quarta Seira mine near the town of Sabugal in the Guarda district, Portugal. It is an approved mineral species by the International Mineralogical Association (IMA). ## Uses Due to its rarity and small accumulations, sabugalite has no industrial application as a uranium ore. However, it is a valued and sought-after mineral by advanced collectors due to its intense color, characteristic crystal forms, and strong fluorescence.

Properties

Mohs hardness: 2.5
Luster: Waxy
Streak: Light yellow
Density: 3.2
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification The most important diagnostic features of sabugalite are its intensely lemon-yellow color, the formation of thin, square tabular crystals, and very strong, greenish-yellow fluorescence under UV light. Its occurrence in paragenesis with other secondary uranium minerals is also a key indicator. ## Distinguishing from Similar Minerals Sabugalite can be confused with other secondary, yellow uranium minerals, such as autunite, meta-autunite, or uranophane. - **Autunite** has a very similar appearance and fluorescence, but crystallizes in the tetragonal system and often forms thicker, better-formed crystals. Definitive distinction requires advanced studies (XRD). - **Uranophane** and **beta-uranophane** have a similar color, but form acicular or fibrous aggregates and crystallize in the monoclinic system. Their fluorescence is usually weaker or absent. ## Crystal Forms Sabugalite crystallizes as very thin, tabular crystals with a square or rectangular outline. These crystals often group into fan-like or rosette-like aggregates. It also commonly occurs as microcrystalline coatings and efflorescences on rocks.

Geological environment

## Genesis Sabugalite is a secondary mineral, forming in the oxidation (weathering) zones of uranium-bearing deposits. It forms as a result of the action of phosphate-rich waters on primary uranium minerals, such as uraninite. It most commonly occurs in fractures and on the surfaces of granitic rocks, pegmatites, and some sandstones. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals, such as autunite, meta-autunite, torbernite, metatorbernite, saleeite, as well as phosphuranylite, uranophane, and gummite. Associated minerals may also include quartz, muscovite, and clay minerals. ## Localities The most important and classic sabugalite localities are in Portugal, in the Sabugal region (Mina da Quarta Seira) and Guarda. Known occurrences have also been reported in Spain (Saelices el Chico deposits in Salamanca), France (e.g., in the Massif Central), Germany (Black Forest), and also in the USA, mainly in Utah, Nevada, and Wyoming. It also occurs in small quantities in uranium deposits in Australia.

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp crystals of intense, lemon-yellow color. Rich coatings on a contrasting rock matrix are also highly prized, especially those forming aesthetic, rosette-like or fan-like aggregates. Large crystal size, though rare for this mineral, significantly increases the value of the specimen. The intensity of fluorescence is also important. ## Popular Localities Reference specimens, considered the best for this species, come from the type locality in Sabugal, Portugal. High-quality crystals have also been obtained from uranium mines in Spain, especially in the Salamanca region. American specimens, e.g., from Utah, are also present on the collector's market, although they often appear as finer crystals or coatings.

Care and storage

## Cleaning Sabugalite is an extremely delicate, brittle, and water-soluble mineral. It must absolutely not be cleaned with water. The only safe method for removing dust is to use a soft brush or a gentle stream of compressed air from a distance. ## What to Avoid Contact with water and other liquids, which can dissolve or damage the crystals, must be strictly avoided. This mineral is sensitive to heat and can lose structural water (dehydration), leading to its destruction. It should be protected from direct sunlight, which can cause fading. Due to its radioactivity, direct skin contact should be avoided, dust should not be inhaled, and hands should be washed after each contact. ## Storage Sabugalite specimens should be stored in a dry place, in a tightly sealed container (e.g., a "perky box"), to protect them from moisture and mechanical damage. Due to its radioactivity, it should be stored away from areas of constant human presence, in a labeled container, preferably in a ventilated display case.

Sources

IMA Mineral List (CNMNC)