Renardite

Chemical formula: Pb₂+(U₆+O₂)₄(PO₄)₂(OH)₄·₇H₂O

Renardite is a rare, highly radioactive secondary uranium mineral, forming aggregates of small, yellow, platy crystals.

## Characteristics Renardite is a hydrated uranyl lead phosphate, belonging to the group of uranium minerals. It occurs in the oxidation zones of uranium deposits, where it forms as a product of uraninite alteration. It typically forms aggregates of small, platy or lamellar crystals, which can arrange into rosette-like or fan-shaped aggregates. Specimens have an intense, lemon-yellow to golden-yellow color and are prized by specialized collectors of uranium minerals. ## Physical Properties Renardite crystals are very small and brittle. The mineral is characterized by a vitreous or slightly silky luster on crystal surfaces, and may be pearly on cleavage planes. It is a relatively soft mineral, with a hardness of about 3.5 on the Mohs scale. Its density is high, which is typical for minerals containing uranium and lead, and is approximately 4.35 g/cm³. ## Colors and Varieties Renardite occurs in characteristic shades of yellow – from lemon-yellow, through golden-yellow, to yellowish-brown. No named color varieties or trade names are distinguished for it. ## History and Name The mineral was first described in 1928 by the Belgian mineralogist Alfred Schoep. He named it in honor of Alphonse-François Renard (1842-1903), a Belgian geologist and petrographer from Ghent University, in recognition of his contributions to the study of igneous and metamorphic rocks of Belgium. ## Uses Due to its rarity and occurrence in small quantities, renardite has no industrial application. It is of purely scientific and collectible significance, being a sought-after specimen in specialized collections of radioactive minerals.

Properties

Mohs hardness: 3.5
Luster: Vitreous, Pearly, Silky
Streak: Pale yellow
Density: 4.35
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Renardite can be identified by its intense yellow color, characteristic platy or lamellar crystal habit, often forming fan-shaped aggregates. A key diagnostic feature is its strong radioactivity, easily detectable with a Geiger counter. It occurs in paragenesis with other secondary uranium minerals. ## Distinguishing from Similar Minerals Renardite is visually very similar to many other secondary uranium minerals, especially phosphates and arsenates. It can be confused with dewindtite, with which it often co-occurs and is structurally related. However, dewindtite has a lighter, canary-yellow color. Final differentiation from other "yellow uranium minerals" (such as autunite, torbernite, carnotite) requires advanced chemical analyses (EDS) or X-ray diffraction (XRD). ## Crystal Forms Renardite crystals are usually very small, with a platy or lamellar habit, flattened parallel to the plane of perfect cleavage. They often form fan-shaped, radial, or rosette-like aggregates, as well as coatings and efflorescences on the host rock.

Geological environment

## Genesis Renardite is a secondary mineral, forming in the oxidation (weathering) zone of hydrothermal and sedimentary uranium deposits. It forms as a result of the alteration of primary uranium minerals, mainly uraninite, in the presence of phosphate- and lead-rich waters. Lead can originate from the radiogenic decay of uranium in uraninite or from the oxidation of co-occurring galena. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. Its most common associates are dewindtite, torbernite, autunite, phosphuranylite, curite, kasolite, as well as primary uraninite. It can also occur in association with galena, pyrite, and quartz. ## Localities The most important and type locality for renardite is the Shinkolobwe mine in Haut-Katanga Province, Democratic Republic of Congo, from where the best specimens originate. It is also known from several other localities worldwide, including the South Alligator mine in the Northern Territory, Australia, and the Lake Athabasca area in Saskatchewan, Canada.

Rarity

Rare

For collectors

## Quality Criteria The most prized renardite specimens are characterized by well-formed, sharp crystals with an intense, golden-yellow color. Rich aggregates forming aesthetic, fan-shaped or rosette-like formations on a contrasting rock matrix are highly valued. Crystal size is also important, although they rarely exceed a few millimeters. The purity of the specimen and the absence of mechanical damage to the brittle crystals significantly increase its value. ## Popular Localities By far the most sought-after renardite specimens by collectors come from its type locality - the Shinkolobwe mine in the Democratic Republic of Congo. Specimens from this location are considered the global standard for this mineral.

Care and storage

## Cleaning Renardite specimens should generally not be wet cleaned. Small, brittle crystals can suffer mechanical damage. Dust can be removed very carefully with a soft brush or a stream of compressed air from a safe distance. ## What to Avoid Renardite is a highly radioactive mineral. Inhaling dust and direct skin contact must be strictly avoided. Washing hands after each contact is mandatory. It should not be stored in areas of permanent human presence (desks, bedrooms). All chemicals, acids, and water, which can damage it, should be avoided. ## Storage Specimens should be stored in tightly sealed, labeled containers (e.g., "perky box" type), away from other radiation-sensitive minerals. Containers should be placed in a dedicated, well-ventilated display cabinet or cupboard, away from work and resting areas. Lead shielding is recommended for larger or more numerous collections of uranium minerals.

Sources

IMA Mineral List (CNMNC)