Gauthierite
Chemical formula: KPb<sup>2+</sup>[(U<sup>6+</sup>O<sub>2</sub>)<sub>7</sub>O<sub>5</sub>(OH)<sub>7</sub>]·8H<sub>2</sub>O
Gauthierite is a very rare, orange uranyl mineral, known for its unique, acicular crystals and intense radioactivity.
Properties
- Mohs hardness
- 2-3
- Luster
- Vitreous to silky
- Streak
- Light orange
- Density
- 5.43
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Characteristic features of gauthierite include its intensely orange color, acicular crystal habit forming radial aggregates, and occurrence in paragenesis with other secondary uranium minerals. The mineral also exhibits pale green fluorescence under ultraviolet light (both longwave and shortwave). However, definitive identification requires advanced analytical methods such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other orange, secondary uranium minerals with an acicular habit, such as becquerelite or curite. Distinguishing them "by eye" is practically impossible. Curite is usually darker (orange-red), and becquerelite has a slightly different hue (yellow-orange), but these differences are subtle and often ambiguous without chemical analysis. ## Crystal Forms Crystals are strongly elongated, prismatic to acicular, often flattened. They usually form radial, stellate, or chaotic aggregates. Single, well-formed crystals are extremely rare.
Geological environment
## Genesis It is a secondary mineral, forming in the oxidation zone (weathering) of uraninite deposits. It forms as a result of the alteration of uraninite under the influence of waters rich in potassium and lead. It occurs in cavities and fissures of uranium-rich rocks. ## Mineral Associations It most often co-occurs with uraninite (as the primary mineral) and other secondary uranyl minerals, such as soddyite, curite, becquerelite, kasolite, and also with quartz. ## Localities The only confirmed and described occurrence of gauthierite in the world is its type locality – the Shinkolobwe mine in Haut-Katanga Province in the Democratic Republic of Congo. This is historically one of the most important uranium deposits in the world.
Rarity
Extremely rare
For collectors
## Quality Criteria Specimens with clearly formed, radial aggregates of intense, orange color, contrasting with the rock matrix, are most highly valued. Due to their microscopic nature, the quality of the photograph (photomicrograph) accompanying the specimen is crucial. The size of the aggregates and the lack of damage to the delicate needles significantly increase their value. ## Popular Localities The only source of specimens is the Shinkolobwe mine. As the mine has been closed and inaccessible for years, all specimens on the market come from old collections (so-called "old-timers"), which makes them even rarer and more desirable.
Care and storage
## Cleaning Gauthierite specimens should not be wet cleaned. Dust can only be removed with a soft brush or a photographic air blower. Any mechanical cleaning is highly risky due to the brittleness and small size of the crystals. ## What to Avoid Contact with water, chemicals, acids, and ultrasound should be absolutely avoided. The mineral is sensitive to changes in temperature and humidity. As a uranium mineral, it is strongly radioactive – direct, prolonged contact, inhalation of dust, and storage near areas of permanent human presence should be avoided. ## Storage Specimens should be stored in sealed, labeled containers (e.g., micromount type), protecting them from mechanical damage and dusting. Due to radioactivity, it is recommended to keep specimens in special containers with a lead lining, away from other radiation-sensitive minerals and photosensitive materials.