Krettnichite
Chemical formula: Pb<sup>2+</sup>Mn<sup>3+</sup><sub>2</sub>(V<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>2</sub>
Krettnichite is an extremely rare mineral from the vanadate group, forming black, tabular crystals with a submetallic luster.
Description
## Characteristics Krettnichite is a rare, hydrated lead and manganese vanadate. It forms very small, thin, tabular or bladed crystals, rarely exceeding 1 mm in length. They most often occur as radial aggregates and rosettes, less frequently as single, scattered flakes on the host rock. The mineral is completely opaque and is characterized by a black color and a submetallic luster, which may appear dull on some surfaces. ## Physical properties The luster of krettnichite is described as submetallic. It is a brittle mineral with a calculated density of 4.89 g/cm³. Its Mohs hardness has not yet been precisely determined. It exhibits perfect cleavage in one plane, which accounts for its tabular appearance. ## Colors and varieties This mineral is monochromatic – it occurs exclusively in black. No color or commercial varieties are known. ## History and name Krettnichite was recognized as a new mineral species by the International Mineralogical Association (IMA) in 1998. Its formal scientific description was published a year later. The name comes from the village of Krettnich in the municipality of Wadern (Saarland, Germany), near which its type locality, the "Glücksstern" manganese mine, is located. ## Applications Due to its extreme rarity and occurrence in microscopic quantities, krettnichite has no industrial application. It is solely an object of scientific and collecting interest.
Diagnostic features
## Identification Key diagnostic features of krettnichite include its black color, submetallic luster, characteristic form of thin, tabular crystals, and tendency to form radial aggregates and rosettes. A brownish-black streak and high density are also helpful. However, definitive identification is almost exclusively possible using advanced analytical methods (XRD, EDS). ## Distinguishing from similar minerals Krettnichite can be confused with other black manganese minerals, such as goethite, pyrolusite, hollandite, or coronadite, which often co-occur with it. Distinguishing it with the naked eye is very difficult, and often impossible. The characteristic crystal habit in the form of rosettes is the best visual clue, but it is not always well-developed. ## Crystal forms Crystals are thin, tabular or bladed, with a rectangular or hexagonal cross-section. They typically form fan-shaped or radial aggregates and elegant rosettes. They are rarely found as single, isolated crystals.
Geological environment
## Genesis Krettnichite is a secondary mineral, forming in the oxidation zones of hydrothermal manganese ore deposits. It forms as a result of the weathering of primary ore minerals under conditions of low temperatures and pressures. ## Mineral associations It most often co-occurs with other manganese oxides and hydroxides, such as goethite, pyrolusite, and coronadite. Mottramite also accompanies it at the type locality. ## Localities This is a mineral with extremely limited occurrence. The most important and practically sole source of well-formed specimens is its type locality – the former "Glücksstern" manganese mine near Krettnich in Saarland (Germany). It has also been reported in the nearby "Frühlings-Anfang" mine.
Rarity
Extremely rare
Collector aspects
## Quality criteria The most highly valued krettnichite specimens are those with sharp, well-formed rosettes or rich, radial crystal aggregates. Contrast with a light host rock significantly enhances visual appeal. Due to the microscopic nature of the mineral, the size of the crystals and aggregates is a key factor influencing value. ## Popular localities The only place in the world from which specimens of collector significance originate is the area of its type locality in Saarland, Germany. Specimens from this location are a rarity on the market and constitute a valuable acquisition for specialized collectors of rare minerals and micromounts.
Care and storage
## Cleaning Krettnichite specimens should be cleaned with the utmost care, preferably dry using a soft brush to remove dust. If necessary, a brief rinse in distilled water is permissible, followed by immediate and thorough drying. The crystals are very brittle and easily damaged. ## What to avoid Ultrasonic cleaners, chemical agents (especially acids), and strong jets of water should be absolutely avoided. The mineral contains lead, so hands should be washed after each contact with the specimen. It should be protected from impacts and abrasion. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust, light, and mechanical damage. Each specimen should be properly labeled, taking into account its toxicity.