Quenselite
Chemical formula: Pb<sup>2+</sup>Mn<sup>3+</sup>O<sub>2</sub>(OH)
Quenselite is a very rare lead manganese oxyhydroxide, forming small, black, tabular crystals with a metallic luster.
Description
## Characteristics Quenselite is a rare mineral from the oxide group, chemically classified as a lead manganese oxyhydroxide. It occurs as small, thin, tabular or platy crystals, often with a pseudohexagonal outline. These crystals typically form visually attractive rosette-shaped aggregates, as well as parallel or subparallel arrangements of plates. The mineral is black and characterized by a strong, metallic or submetallic luster on crystal surfaces. It is completely opaque. ## Physical Properties Quenselite is relatively soft, with a Mohs hardness of 2.5, meaning it can be scratched with a fingernail. It has a very high density, ranging from 6.85 to 6.88 g/cm³, which is a result of its high lead content. The luster is metallic to submetallic, and the mineral is opaque. It exhibits perfect cleavage in one direction, causing it to easily split into thin lamellae. ## Colors and Varieties This mineral is monochromatic – it occurs exclusively in black. No color or commercial varieties are known. ## History and Name Quenselite was first described in 1925 by Gustaf Flink. The mineral was named in honor of Percy Dudgeon Quensel (1881-1966), a professor of mineralogy at Stockholm University, Sweden. The type locality, from which the first described specimens originated, is the famous Långban deposit in Filipstad Municipality, Värmland County, Sweden. ## Uses Due to its extreme rarity, quenselite has no industrial applications. It is solely an object of scientific interest and a prized acquisition for advanced mineral collectors, especially those specializing in rare species or minerals from Långban.
Diagnostic features
## Identification Characteristic features of quenselite include its black color, metallic luster, very high density (the specimen feels unnaturally heavy for its size), and perfect cleavage in one direction. The typical habit of thin, tabular crystals, often in rosette aggregates, is also an important diagnostic clue. ## Distinguishing from Similar Minerals Quenselite can be confused with other black manganese minerals, such as hausmannite, with which it often co-occurs. However, hausmannite crystallizes in the tetragonal system and does not exhibit the same perfect cleavage as quenselite. Its very high density, resulting from the presence of lead, also distinguishes it from other manganese oxides. ## Crystal Forms Quenselite forms thin, tabular or platy crystals with a pseudohexagonal outline. These crystals rarely occur individually, most often forming fan-shaped or rosette aggregates. Clusters of small, parallelly arranged plates are also found.
Geological environment
## Genesis Quenselite is a rare secondary mineral, formed as a result of metamorphic processes in iron and manganese ore deposits. In its type locality (Långban), it occurs in fissures and cavities in calcite or in association with hausmannite. ## Mineral Associations This mineral most commonly co-occurs with minerals such as hausmannite, calcite, barite, pyrochroite, manganite, and other rare oxide and silicate minerals typical of the Långban deposit. ## Localities The most important and historically first locality of quenselite, from which most of the best collector specimens originate, is the Långban deposit in Värmland, Sweden. This mineral has also been identified in several other genetically similar manganese deposits worldwide, for example, in the Jakobsberg mine in Sweden, but it remains an extremely rare mineral.
Rarity
Very rare
Collector aspects
## Quality Criteria The most highly prized quenselite specimens are those with well-formed, sharp crystals forming aesthetic rosettes. The size of the crystals is of great importance – the larger they are, the more valuable the specimen. A contrasting background, such as white calcite, on which black, shiny quenselite aggregates are set, also enhances its attractiveness. Specimens without mechanical damage and with a distinct luster are the most sought after. ## Popular Localities The vast majority, if not all, quenselite specimens available on the collector's market come from one place in the world: the historic Långban deposit in Sweden. This is the classic locality for this mineral, and specimens from there are considered exemplary.
Care and storage
## Cleaning Quenselite crystals are soft and delicate. For dust removal, it is best to use a soft brush or compressed air from a safe distance. If necessary, the specimen can be rinsed in distilled water using a very soft brush, and then immediately dried. Ultrasonic cleaners should be avoided. ## What to Avoid The mineral is very soft (hardness 2.5) and has perfect cleavage, making it susceptible to any impacts, scratches, and pressure. Contact with acids and other aggressive chemicals should be avoided. Due to its lead content, it is recommended to wash hands after handling the mineral. ## Storage Quenselite specimens are best stored in separate, padded boxes (e.g., "micromount" type) to protect them from mechanical damage and dust. It does not require special conditions regarding light or humidity, but it should be kept away from specimens that could scratch it.