Aldridgeite
Chemical formula: (Cd<sup>2+</sup>,Ca)(Cu<sup>2+</sup>,Zn<sup>2+</sup>)<sub>4</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>·3H<sub>2</sub>O
Aldridgeite is a very rare, hydrated cadmium and copper sulfate, forming characteristic blue aggregates of radial crystals.
Description
## Characteristics Aldridgeite is a mineral from the sulfate group, chemically classified as a hydrated cadmium, calcium, copper, and zinc sulfate. It forms small, acicular or prismatic crystals, most often occurring as radial or divergent aggregates, resembling fans or bundles. Its most characteristic visual feature is an attractive, light blue to greenish-blue color. ## Physical Properties This mineral is relatively soft, with a hardness of about 3 on the Mohs scale. It has a vitreous luster and is transparent to translucent. Its density, calculated based on its chemical composition and crystal structure, is approximately 3.43 g/cm³. It is brittle and exhibits good cleavage in one plane. ## Colors and Varieties Aldridgeite occurs in a uniform color range, from light blue to blue-green. No distinct color varieties or commercial names have been identified. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2009. Its name comes from its discovery locality – the Aldridge mine in British Columbia, Canada, which is its type locality. It was first described in 2011. ## Applications Due to its extreme rarity and small crystal size, aldridgeite has no industrial applications. It is solely an object of scientific interest and a prized acquisition in advanced collections of systematic and rare minerals.
Diagnostic features
## Identification Characteristic features of aldridgeite include its light blue color, vitreous luster, and typical occurrence in the form of radial aggregates composed of acicular crystals. Its environment of occurrence is also crucial – oxidation zones of sulfide deposits, often in association with other secondary sulfates. ## Distinguishing from similar minerals Aldridgeite can be confused with other blue or green secondary copper minerals, such as ktenasite, spangolite, or aurichalcite. It differs from ktenasite in crystal habit, and from spangolite and aurichalcite in the different form of aggregates. Certain differentiation from visually similar minerals often requires advanced studies, including chemical analysis to confirm the presence of cadmium. ## Crystal forms Crystals are acicular to prismatic. They almost always occur as aggregates: radial, divergent, fan-shaped, or forming small, reniform clusters with a radial internal structure.
Geological environment
## Genesis Aldridgeite is a secondary mineral, formed in the oxidation zones of polymetallic sulfide deposits. It forms in post-mining conditions, as a result of the weathering of primary ores containing cadmium (mainly sphalerite) and copper. It forms at low temperatures from sulfate-rich solutions. ## Mineral associations This mineral co-occurs with other secondary sulfates, such as ktenasite, spangolite, devilline, brochantite, as well as gypsum and relict sphalerite. ## Localities The most important and only well-documented location for high-quality aldridgeite specimens is its type locality – the Aldridge mine in Creston, British Columbia (Canada).
Rarity
Very rare
Collector aspects
## Quality criteria The most highly prized aldridgeite specimens are characterized by an intense, pure blue color and well-formed, distinct radial aggregates. The size and aesthetics of these aggregates on the rock matrix are of great importance. Specimens free from damage, with a minimal amount of gangue, achieve the highest value. Association with other rare secondary minerals also enhances their attractiveness. ## Popular localities The only source of collector specimens is the Aldridge mine in British Columbia, Canada. Minerals from this locality are considered exemplary for the species.
Care and storage
## Cleaning Aldridgeite specimens should be cleaned very carefully, using only a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Ultrasonic cleaners are absolutely not recommended. ## What to avoid As a hydrated sulfate, aldridgeite is sensitive to high temperatures, which can lead to its dehydration and structural damage. It should be protected from all acids and other strong chemicals. Due to its low hardness, it is susceptible to scratching. ## Storage It is recommended to store specimens in stable conditions, away from direct sunlight, heat sources, and sudden changes in humidity. The safest way is to place the mineral in a sealed collector's box or display case, which protects it from mechanical damage and dust.