Lepageite
Chemical formula: Mn<sup>2+</sup><sub>3</sub>(Fe<sup>3+</sup><sub>7</sub>Fe<sup>2+</sup><sub>4</sub>)O<sub>3</sub>[Sb<sup>3+</sup><sub>5</sub>As<sup>3+</sup><sub>8</sub>O<sub>34</sub>]
Lepageite is an extremely rare iron and manganese arsenate-antimonate, forming black, metallic, acicular crystals known from only one locality in the world.
Properties
- Luster
- Metallic
- Streak
- Black
- Density
- 5.43
- Transparency
- Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identifying lepageite based on visual characteristics is practically impossible and requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS). Preliminary indications may include its black color, metallic luster, acicular crystal form creating radial aggregates, and, most importantly, its origin from the only known locality. ## Distinguishing from Similar Minerals Lepageite can be confused with other black, acicular minerals found in Franklin, such as some sulfosalts or oxides. Without specialized equipment, it cannot be distinguished from co-occurring löllingite or arsenopyrite. Definitive differentiation is only possible based on chemical composition analysis. ## Crystal Forms Lepageite crystals have an acicular or fibrous habit. They almost always occur in aggregates – most often radial (spreading from a common center) or fan-shaped.
Geological environment
## Genesis Lepageite forms in a unique environment of a metamorphosed, stratiform zinc, iron, and manganese ore deposit. It is a secondary mineral, crystallizing in the late stage of hydrothermal processes that altered the primary ore sediments. Its formation is associated with a high concentration of arsenic, antimony, iron, and manganese under the specific conditions prevailing in the Franklin deposit. ## Mineral Associations This mineral occurs in paragenesis with other, often rare, minerals from the Franklin deposit. It is most commonly associated with arsenopyrite, löllingite, andyrobertsite, sterlinghillite, as well as zincite and willemite. ## Localities The only confirmed occurrence of lepageite in the world is its type locality – the Fletcher Mine, in Franklin, Sussex County, New Jersey, USA. It is an endemic mineral to this single deposit.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a lepageite specimen is primarily determined by the very possibility of its identification. Highly valued samples are those where well-formed, radial aggregates of acicular crystals are visible, preferably set on a contrasting matrix (e.g., on white calcite). Co-occurrence with other rare minerals from Franklin adds significant value, enhancing the scientific and aesthetic appeal of the specimen. ## Popular Localities The only source of lepageite specimens is historical collections from the Fletcher Mine in Franklin, New Jersey, USA. The mine has long been inactive, and no new material is being acquired, making every existing specimen unique.
Care and storage
## Cleaning Lepageite specimens are extremely delicate and susceptible to mechanical damage. Cleaning should be limited to an absolute minimum. Only very careful removal of dust with a stream of compressed air from a safe distance is permissible. Any contact with water, chemicals, or brushes should be avoided. ## What to Avoid The mineral contains arsenic and antimony, which are toxic elements. Avoid inhaling dust and wash hands after any contact with the specimen. It must not be heated or exposed to acids and other chemicals. Brittle, acicular crystals are easily destroyed, so vibrations, shocks, and touching should be avoided. ## Storage It is recommended to store lepageite specimens in sealed, closed containers (such as "micromount boxes") that protect against dust, moisture, and mechanical damage. The container should be clearly labeled with information about the mineral's toxicity.