Decrespignyite-(Y)

Chemical formula: Y₄Cu²⁺(CO₃)₄Cl(OH)₅·₂H₂O

De Crespignyite-(Y) is a rare hydrated copper and yttrium carbonate, distinguished by its intense blue color and occurrence as small, radial aggregates.

## Characteristics De Crespignyite-(Y) is a mineral from the carbonate group, visually presenting as aggregates of small, bladed crystals forming rosettes and radial aggregates. Individual crystals rarely exceed 1 mm in length. This mineral is valued for its vivid, royal-blue color, which can transition into lighter, sky-blue shades. It typically occurs in small quantities, forming thin coatings and crusts on the surface of the host rock. ## Physical Properties The mineral is characterized by a Mohs hardness of 4. Its density is approximately 3.64 g/cm³. The luster is described as vitreous to pearly, especially visible on the surfaces of individual crystals within aggregates. It is a translucent mineral. ## Colors and Varieties The dominant and only known color of de Crespignyite-(Y) is an intense blue, ranging from pale blue to a deep, royal shade. No color or commercial varieties are distinguished. ## History and Name The mineral's name honors Robert Champion de Crespigny (born 1950), an Australian businessman and philanthropist, for his contributions to the development of the mining industry and education in South Australia. The mineral was described in 2002 by K. Wallwork, U. Kolitsch, A. Pring, and L. Nasdala. The suffix "-(Y)" indicates the dominance of yttrium in its chemical composition. ## Applications Due to its extreme rarity and occurrence in small quantities, de Crespignyite-(Y) has no industrial applications. It is of purely scientific and collector's interest.

Properties

Mohs hardness: 4
Luster: Vitreous to pearly
Streak: pale blue
Density: 3.64
Cleavage: No cleavage was observed but the morphology suggests that cleavage would be on {010}.
Fracture: None observed
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features include its intense blue color and characteristic occurrence as radial aggregates and rosettes composed of small, bladed crystals. A pale blue streak is also helpful for identification. However, definitive confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals De Crespignyite-(Y) can be confused with other secondary blue copper minerals, such as azurite, cyanotrichite, or linarite. Azurite typically forms larger, better-formed crystals and has a darker color. Cyanotrichite occurs as acicular, felt-like aggregates. Linarite has a similar color but crystallizes differently and is denser. ## Crystal Forms De Crespignyite-(Y) crystals are very small, bladed, and flattened. They combine into radial aggregates, rosettes, and spherulitic clusters, forming thin coatings on the rock.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation (weathering) zones of copper ore deposits. It forms as a result of hydrothermal solutions acting on rocks rich in copper and rare earth elements, especially yttrium. ## Mineral Associations This mineral co-occurs with other secondary copper and lead minerals. At its type locality, it was found in association with malachite, brochantite, cerussite, chalcopyrite, quartz, as well as rare minerals like kamphaugite-(Y) and donnayite-(Y). ## Localities The only confirmed and described occurrence of de Crespignyite-(Y) is its type locality – the Paratoo copper mine in the Flinders Ranges region of South Australia. This is the only known locality for this mineral in the world.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized specimens are those with rich, well-formed aggregates of intensely saturated, royal-blue color. Contrast with the light host rock (matrix) and the absence of damage to delicate crystals are also important. Due to the microscopic size of the crystals, specimens are primarily evaluated based on the aesthetics of the entire aggregate. ## Popular Localities The only source of de Crespignyite-(Y) specimens is the Paratoo mine in South Australia. Material from this locality is extremely rare and sought after by specialized collectors of rare minerals and "micromounts."

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Any contact with water or other liquids is inadvisable due to the delicate nature of the mineral and the risk of damage. Ultrasonic or steam cleaners should not be used. ## What to Avoid Avoid contact with all chemicals, including acids and bases, which can destroy the mineral. Protect it from high temperatures, direct sunlight, which can cause fading, and moisture. It is a brittle mineral, sensitive to impacts and scratches. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "micromount" boxes), protecting them from dust, moisture, and mechanical damage. Display should be in controlled conditions, away from sources of light and heat.