Parauranophane

Chemical formula: Ca(U⁶⁺O₂)₂(SiO₃OH)₂(H₂O)₄·H₂O

Parauranophane is a hydrated uranyl calcium silicate, forming characteristic, acicular crystals of an intensely yellow color.

## Characteristics Parauranophane is a secondary mineral from the uranophane group, belonging to the silicates. It occurs in the oxidation zones of uranium ore deposits. It forms characteristic aggregates in the form of radial or tangled masses, as well as crusts and coatings. Well-formed crystals appear as small, elongated needles or blades, often gathered into fan-shaped or stellate structures. Due to its uranium content, it is a highly radioactive mineral. ## Physical Properties Parauranophane crystals are brittle and delicate. The Mohs hardness is 2.5-3. The luster is typically vitreous, and on some surfaces, it can be waxy. The mineral is transparent to translucent. ## Colors and Varieties Parauranophane most often exhibits colors ranging from yellow and yellowish-green to yellowish-brown. The intensity and hue depend on the specific chemical composition and impurities. No named commercial or color varieties are distinguished. ## History and Name The mineral's name refers to its structural and chemical similarity to uranophane, with the prefix "para-" indicating a different crystal structure (polymorphism). It was first described in 1935. Jáchymov in the Czech Republic was designated as the type locality (place of first discovery). ## Uses Parauranophane, like other secondary uranium minerals, is primarily of scientific and collector's interest. It serves as an indicator of the presence of primary uranium deposits. Due to its radioactivity and brittleness, it has no practical industrial application.

Properties

Mohs hardness: 2.5-3
Luster: Vitreous, Waxy
Density: 0
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of parauranophane are its intensely yellow or yellowish-green color, acicular crystal habit, and occurrence in radial aggregates or crusts. The mineral exhibits strong, green fluorescence under ultraviolet light (both shortwave and longwave). The most important characteristic is its high radioactivity, easily measurable with a Geiger counter. ## Distinguishing from Similar Minerals Parauranophane is difficult to distinguish from uranophane without advanced studies (e.g., powder X-ray diffraction, XRD), as both minerals have almost identical appearance and physical properties. Uranophane crystallizes in the monoclinic system but often forms the same acicular aggregates. Other secondary uranium minerals, such as autunite or torbernite, typically form tabular, not acicular, crystals. ## Crystal Forms Parauranophane forms elongated, acicular or bladed crystals, which rarely occur individually. Most often, it forms radial, stellate, or chaotically tangled aggregates. It is also commonly found as dense, felt-like masses, crusts, and coatings on host rocks.

Geological environment

## Genesis Parauranophane is a secondary mineral, forming in the weathering (oxidation) zones of uranium ore deposits, mainly uraninite. It forms as a result of the action of silica-rich waters on primary uranium minerals in an oxygen-rich environment. It is a product of relatively low-temperature hydrothermal processes or surface weathering. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. Its most common associations include uranophane, uraninite (as a primary mineral), gypsum, calcite, as well as other uranyl silicates and oxides. ## Localities The most important and classic localities for parauranophane are in the Czech Republic (Jáchymov) and Germany. Significant specimens also come from uranium mines in the Shinkolobwe area of the Democratic Republic of Congo. It also occurs in many uranium deposits in the United States, particularly in the states of Utah, Arizona, and New Mexico.

Rarity

Not very common

For collectors

## Quality Criteria Specimens with well-formed, long, and sharp needles, forming aesthetic, radial or stellate aggregates, are most valued by collectors. An intense, clean color without brown coatings is important. Contrast with a dark host rock (matrix) significantly enhances the visual appeal and value of the specimen. Large, undamaged clusters are rare and sought after. ## Popular Localities Historical localities in Jáchymov (Czech Republic) are considered classic and provide high-quality specimens. Specimens from the Musonoi and Shinkolobwe mines in the Democratic Republic of Congo are also highly prized, often characterized by exceptionally aesthetic crystalline forms.

Care and storage

## Cleaning Parauranophane specimens are extremely delicate and brittle. Mechanical cleaning is not recommended. Only very careful removal of loose contaminants using a soft brush or a stream of compressed air from a safe distance is permissible. Contact with water and any chemicals should be avoided. ## What to Avoid The mineral is sensitive to shocks and pressure – acicular crystals are easily damaged. Contact with acids and other chemical agents must be strictly avoided. As a hydrated mineral, it may undergo changes under conditions of low humidity or elevated temperature. Due to radioactivity, exposure should be limited, and dust inhalation should be avoided. ## Storage Parauranophane requires storage under stable conditions, away from sources of vibration and direct sunlight. The safest method is to place the specimen in a sealed, padded "membrane box" or in a display case away from other, harder minerals. Due to radioactivity, specimens should be stored in a well-ventilated area, inaccessible to children and pets.

External references

https://www.mindat.org/min-4106.html