Melanotekite
Chemical formula: Pb²⁺₂Fe³⁺₂O₂Si₂O₇
Melanotekite is a rare lead iron silicate, forming dark, almost black crystals with a metallic or resinous luster.
Properties
- Mohs hardness
- 6.5
- Color
- Black, dark gray, blackish green
- Luster
- Metallic, Pitchy, Greasy
- Streak
- Grayish-black
- Density
- 5.73
- Cleavage
- Two cleavages are known, but without reported miller indices.
- Fracture
- Uneven, Conchoidal
- Transparency
- Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Melanotekite can be recognized by its characteristic black or dark brown color, resinous or metallic luster, and high density, noticeable even in small specimens. A diagnostic feature is also its occurrence in a specific geological environment, in association with other manganese and lead minerals. ## Distinguishing from Similar Minerals It can be confused with other black, heavy minerals with a similar luster, such as magnetite, ilmenite, or some manganese oxides (e.g., hollandite, pyrolusite). It is distinguished from magnetite by its lack of magnetic properties. Distinguishing it from other minerals without specialized tests (e.g., XRD) can be difficult and often relies on the analysis of associated minerals and knowledge of the locality. ## Crystal Forms Melanotekite crystals are usually small, tabular or short-prismatic. They often form granular, massive, or radial aggregates. Well-formed, single crystals are rare.
Geological environment
## Genesis Melanotekite is a metamorphic mineral. It forms as a result of contact metamorphism of iron and manganese ore deposits, especially in skarns and silica-rich rocks. Its formation is associated with the presence of hydrothermal solutions rich in lead and iron. ## Mineral Associations This mineral co-occurs with other rare minerals, which is crucial for its identification. In its type locality (Långban, Sweden), it has been found in association with baryte, calcite, native lead, kentrolite, and hedyphane. In Franklin (New Jersey, USA), it associates with calcite, willemite, franklinite, andradite, and roeblingite. ## Localities The most important and classic occurrences of melanotekite are the Långban mine in Sweden and the ore deposits in Franklin and Sterling Hill in New Jersey, USA. It is also known from several other places worldwide, including the Kombat mine in Namibia and Broken Hill in Australia, but specimens from these localities are much rarer on the collector's market.
Rarity
Rare
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, sharp crystals with a distinct luster. Rich crystalline aggregates on a contrasting matrix, for example on white calcite, are also highly prized. The locality is key – specimens from classic sites such as Långban and Franklin command higher prices. Crystal size rarely exceeds a few millimeters, so even small but well-formed crystals are considered valuable. ## Popular Localities Specimens from two historical localities are by far the most sought after on the collector's market: Långban in Sweden and Franklin in New Jersey, USA. They represent classics for this mineral and are a benchmark for quality and value.
Care and storage
## Cleaning Melanotekite specimens should be cleaned very carefully, preferably dry using a soft brush to remove dust. If necessary, a damp cloth with distilled water can be used, and then the specimen should be dried immediately. Ultrasonic cleaners should be avoided. ## What to Avoid As a lead-bearing mineral, it is sensitive to acids. Contact with household chemicals and acids should be avoided. It should not be heated. Prolonged exposure to moisture can be harmful. ## Storage It is recommended to store melanotekite in a dry place, in a closed display box or cabinet, to protect it from dust and mechanical damage. Due to the presence of lead in its composition, hands should be washed after contact with the mineral.