Alumolukrahnite
Chemical formula: CaCu<sup>2+</sup>Al(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)(H<sub>2</sub>O)
An extremely rare calcium copper aluminum arsenate, forming microscopic, pale blue crystals in aggregates.
Description
## Characteristics Alumolukrahnite is a hydrated arsenate belonging to the tsumcorite group. It is a secondary mineral, occurring as small radial aggregates or tangled masses. Individual crystals are bladed and reach a maximum length of 0.5 mm, making it a mineral primarily for micromineral collectors. Its characteristic feature is its pale blue color. ## Physical Properties Alumolukrahnite crystals are translucent and exhibit a vitreous luster. The hardness of the mineral has not yet been determined. Its density, calculated from unit cell parameters, is 3.99 g/cm³. ## Colors and Varieties This mineral occurs exclusively in one color – pale blue. No color varieties or commercial forms are known. ## History and Name Alumolukrahnite was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2013. Its name refers to its chemical composition – it is an aluminum (aluminous) analogue of lukrahnite, in which aluminum replaces iron (Fe³⁺). ## Uses Due to its extreme rarity and microscopic crystal size, alumolukrahnite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for specialized systematic collections.
Diagnostic features
## Identification Visual identification is practically impossible due to the microscopic size of the crystals and its rarity. Key features include its pale blue color, radial aggregates composed of bladed crystals, and specific mineral parageneses. Definitive identification requires advanced analytical techniques, such as X-ray diffraction (XRD) or chemical microanalysis (EDS). ## Differentiation from Similar Minerals It can be confused with other pale blue secondary minerals, especially arsenates. It is structurally related to lukrahnite (containing Fe³⁺) and gartrellite (containing Fe³⁺ and Zn). Differentiating these minerals is only possible based on chemical composition analysis. ## Crystal Forms It forms aggregates with a radial structure, consisting of small, bladed crystals, often tangled together.
Geological environment
## Genesis Alumolukrahnite is a secondary mineral that forms in the oxidation zones of polymetallic, hydrothermal ore deposits. ## Mineral Associations It co-occurs with minerals such as quartz, olivenite, schubnelite, prosopite, chenevixite, and crusts of amorphous manganese and iron oxides. ## Localities Its occurrence has been confirmed in only two locations worldwide, both in the Atacama region of Chile. These are the Maria Catalina mine (type locality) and the Veta Negra mine.
Rarity
Extremely rare
Collector aspects
## Quality Criteria For micromount minerals, to which alumolukrahnite belongs, the value of a specimen is primarily determined by the abundance of the mineral on the rock matrix, the degree of development and sharpness of the microcrystals, and the presence of interesting associated minerals. The aesthetics of the entire specimen, including color contrast, also increases its attractiveness. ## Popular Localities The only known sources of specimens are two mines in Chile. The most prized specimens come from the type locality – the Maria Catalina mine in Copiapó province.
Care and storage
## Cleaning Specimens should be cleaned with the utmost care, preferably using a soft, dry brush or a stream of compressed air to remove dust. Avoid contact with water; if necessary, use distilled water and dry the specimen immediately. ## What to Avoid As an arsenate, the mineral is potentially toxic. Avoid inhaling dust and ingestion. After each contact with the specimen, hand washing is recommended. Protect it from contact with acids and other aggressive chemicals. There is no data on its stability in light and temperature, but avoiding extreme conditions is recommended. ## Storage The safest storage method is to place the specimen in a sealed "micromount" box, which protects delicate crystals from mechanical damage, dust, and loss. Each container should be precisely labeled.