Ianthinite

Chemical formula: U<sup>4+</sup><sub>2</sub>(U<sup>6+</sup>O<sub>2</sub>)<sub>4</sub>O<sub>6</sub>(OH)<sub>4</sub>·9H<sub>2</sub>O

A hydrous uranium oxide with a characteristic violet-black color, which is unstable and rapidly oxidizes in air to yellow secondary minerals.

## Characteristics Ianthinite is a secondary uranium mineral, valued for its unique, intense violet to violet-black color. It occurs as small, prismatic or acicular crystals, often forming radial aggregates and crusts. Its most characteristic feature is its instability under oxygenic conditions – it rapidly oxidizes in air, becoming covered with a yellow layer of alteration products, mainly schoepite. For this reason, unaltered ianthinite specimens are rare and sought after. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2-3. It exhibits a luster ranging from submetallic to resinous or greasy. It is opaque, becoming translucent only in very thin fragments. It has perfect cleavage in one direction. ## Colors and Varieties Its color ranges from dark violet and violet-black to bluish-black. It does not form color varieties, but often occurs with its yellow or orange oxidation products, creating striking, bicolored specimens. ## History and Name The mineral's name comes from the Greek word *ianthinos*, meaning "violet," referring to its characteristic color. It was first described in 1926 by Alfred Schoep based on material from the Kasolo mine in Shinkolobwe (Democratic Republic of Congo), which is its type locality. ## Uses Ianthinite has no industrial application. Due to its rarity, unique color, and alteration phenomenon, it is a mineral of purely scientific and collectible importance.

Properties

Mohs hardness
2-3
Luster
Sub-metallic to resinous
Streak
Brownish-black
Density
3.64
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Orthorhombic

Diagnostic features

## Identification The most important diagnostic feature of ianthinite is its unique violet-black color combined with the presence of yellow, powdery coatings of its oxidation products. It is highly radioactive, which can be easily detected with a Geiger counter. It reacts to ultraviolet light, but its fluorescence is usually masked by strongly fluorescent alteration products. ## Distinguishing from Similar Minerals It is distinguished from uraninite by its violet hue (uraninite is black) and crystal habit (ianthinite forms acicular and prismatic crystals, uraninite most often cubic or occurs as massive aggregates). It is distinguished from other dark minerals of the uranium ore oxidation zone by its characteristic alteration and specific color. ## Crystal Forms Ianthinite forms elongated, prismatic or acicular crystals with a rhombic cross-section. They often occur as radial or fan-shaped aggregates. It is also found as fine-grained crusts and coatings.

Geological environment

## Genesis Ianthinite is a secondary mineral, formed in the reducing (anoxic) zone of hydrothermal uranium deposits. It forms as a result of the alteration of primary uraninite under conditions of oxygen deprivation. When conditions change to oxidizing, ianthinite rapidly alters into other, more stable uranium oxides. ## Mineral Associations It most often co-occurs with uraninite (as the parent mineral) and with its own alteration products, such as schoepite, metaschoepite, and becquerelite. Other rare secondary uranium minerals, such as curite, kasolite, or soddyite, may also accompany it. ## Localities The most important and historical locality, from which the best specimens originate, is the Kasolo mine in Shinkolobwe in the Democratic Republic of Congo. It is also known from Jáchymov in the Czech Republic, Wölsendorf in Bavaria (Germany), the Great Bear Lake region in Canada, and some uranium mines in Utah, USA.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued ianthinite specimens are those that have retained their original, deep violet color and have not (or only minimally) altered to yellow schoepite. Well-formed, sharply terminated crystals are sought after, especially those forming striking, radial aggregates. The value of a specimen is also enhanced by its origin from classic localities, such as Shinkolobwe. ## Popular Localities The historical Shinkolobwe mine in the DRC is considered the source of the world's best ianthinite specimens. Specimens from this locality fetch the highest prices and are a highlight of advanced systematic collections. Other prized localities include Jáchymov in the Czech Republic and Canadian deposits near Great Bear Lake.

Care and storage

## Cleaning Ianthinite is an extremely sensitive mineral and should not be cleaned. Any contact with water, or even humid air, accelerates its alteration to yellow schoepite. Mechanical cleaning should be avoided due to its great softness and fragility. ## What to Avoid The greatest threat to ianthinite is contact with atmospheric oxygen. Exposure to air, moisture, direct sunlight, and temperature changes must be strictly avoided. The mineral is highly radioactive and requires specialized precautions when handling and storing it. ## Storage Ianthinite specimens must be stored in sealed, airtight containers to cut off oxygen access. The best method is storage in distilled water or in an inert gas atmosphere (e.g., argon). Due to its strong radioactivity, it should be stored in radiation-shielding containers (e.g., lead-lined), away from other minerals and areas of permanent human presence.

Sources

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