Lindackerite
Chemical formula: Cu<sup>2+</sup><sub>5</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(As<sup>5+</sup>O<sub>3</sub>OH)<sub>2</sub>·9H<sub>2</sub>O
Lindackerite is a rare, hydrated copper arsenate, forming characteristic apple-green radial aggregates and rosettes.
Description
## Characteristics Lindackerite is a rare secondary mineral from the arsenate group. It forms small, platy or acicular crystals, most commonly occurring as radial aggregates, rosettes, or spherical clusters. Crusts and coatings are also common forms of its occurrence. Its most characteristic visual feature is delicate, apple-green rosettes, which can reach several millimeters in diameter. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5-3. It is brittle and has a density of about 3.25 g/cm³. The luster is typically vitreous, and on cleavage surfaces, it can be pearly. It is a translucent mineral. ## Colors and Varieties Lindackerite occurs in shades from whitish, through yellowish-green, to the characteristic, vibrant apple-green. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1853 by Johann Franz Xaver von Zepharovich, honors Joseph Lindacker (1821-1883), a Czech chemist from Jáchymov, who first performed its chemical analysis. The type locality is Jáchymov (St. Joachimsthal) in the Czech Republic. ## Applications Lindackerite has no industrial applications. It is solely a mineral of scientific and collector's interest, valued for its rarity and aesthetic forms.
Diagnostic features
## Identification Key diagnostic features of lindackerite are its apple-green color, characteristic forms of occurrence as radial rosettes or spherical aggregates, and its softness. Its paragenesis with other secondary copper and cobalt arsenates in oxidation zones is also an important clue. ## Distinguishing from Similar Minerals Lindackerite is sometimes confused with other green secondary minerals. It is distinguished from annabergite (nickel arsenate) by a slightly different shade of green and paragenesis (annabergite accompanies nickel minerals). It is distinguished from olivenite by lower hardness and different crystal forms (olivenite more often forms single, prismatic crystals). A definitive distinction often requires chemical analysis or detailed crystallographic studies. ## Crystal Forms Crystals are very small, elongated, platy or acicular. They almost never occur as single, well-formed individuals. They typically form radial aggregates, fan-shaped clusters, rosettes, and thin crusts on the host rock.
Geological environment
## Genesis Lindackerite is a secondary mineral, formed in the oxidation zones of polymetallic ores rich in arsenic and copper. It forms as a result of the weathering of primary sulfides and arsenides, such as chalcopyrite and arsenopyrite, under conditions of low temperatures and pressures. ## Mineral Associations This mineral often co-occurs with other rare secondary minerals. Its typical associations include geminite, lavendulan, picropharmacolite, erythrite, annabergite, and gypsum. ## Localities The most important and historical locality is its type locality – Jáchymov in the Czech Republic. It is also known from several places in Germany, including mines in the Odenwald region (Hesse) and the Clara mine in the Black Forest. It has also been reported in Switzerland (Valais canton).
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly prized lindackerite specimens are those with well-formed, distinct rosettes of intense, apple-green color. The absence of damage to the delicate crystals and the aesthetic placement of the aggregates on a small, contrasting rock matrix are important. Specimens with rare associated minerals also increase in value. ## Popular Localities Classic and most sought-after specimens by collectors come from Jáchymov in the Czech Republic. Well-formed aggregates from the German Clara mine are also highly valued.
Care and storage
## Cleaning Extreme caution should be exercised. The safest method is dry cleaning using a soft brush or compressed air from a safe distance. Due to the water content in its structure, prolonged contact with water should be avoided. If absolutely necessary, a very brief rinse in distilled water and immediate, thorough drying is permissible. ## What to Avoid As an arsenate, lindackerite is toxic – avoid inhaling dust and wash hands after any contact with specimens. The mineral is soft, brittle, and has perfect cleavage, making it very susceptible to mechanical damage. Ultrasonic cleaners, all chemicals, and acids should be avoided. It is sensitive to high temperatures, which can cause dehydration and structural damage. ## Storage Lindackerite specimens are best stored in closed, padded boxes or display cases to protect them from dust, light, and mechanical damage. Stable humidity and temperature conditions should be maintained.