Nelenite
Chemical formula: Mn<sup>2+</sup><sub>16</sub>As<sup>3+</sup><sub>3</sub>Si<sub>12</sub>O<sub>36</sub>(OH)<sub>17</sub>
Nelenite is a rare, brown manganese arsenosilicate, forming massive aggregates, closely related to pyrochroite and friedelite.
Properties
- Mohs hardness
- 5
- Luster
- Vitreous to resinous
- Streak
- Pale yellow to yellowish-brown
- Density
- 3.46-3.52
- Cleavage
- Good on {0001}
- Fracture
- Uneven
- Transparency
- Translucent to opaque
- Crystal system
- Trigonal
Diagnostic features
## Identification Nelenite is primarily identified by its brown color, massive habit, and specific occurrence environment - in manganese deposits. Its streak - pale yellow to yellowish-brown - is also characteristic. However, definitive identification requires advanced analytical methods, such as chemical analysis (EDS) or X-ray diffraction (XRD), due to its similarity to other manganese minerals. ## Distinguishing from Similar Minerals Nelenite can be confused with other manganese minerals of similar color and habit, such as friedelite, pyrochroite, or hausmannite. Friedelite is usually more reddish and often exhibits better cleavage. Pyrochroite has lower hardness (approx. 2.5). Hausmannite is harder (5.5) and has a darker, reddish-brown to black streak. ## Crystal Forms Nelenite most often forms massive, compact, or fine-grained aggregates. Very rarely, poorly formed, small crystals with a hexagonal outline, grouped in rosette-like aggregates, are observed.
Geological environment
## Genesis Nelenite is a mineral of metamorphic origin. It forms as a result of the metamorphism of manganese ore deposits, especially in silica-rich rocks. It occurs in layers and lenses within franklinite and willemite. ## Mineral Associations This mineral coexists with other manganese and zinc minerals. Its most common associations include: franklinite, willemite, rhodochrosite, andradite (manganese variety), calcite, baryte, hausmannite, friedelite, and pyrochroite. ## Localities The most important and classic locality for nelenite is the Trotter Mine in Franklin, Sussex County, New Jersey, USA. This is its type locality. It is also known from the nearby Sterling Hill deposit in Ogdensburg. Outside the USA, its presence has been reported in the Kombat Mine in Namibia.
Rarity
Rare
For collectors
## Quality Criteria The collectible appeal of nelenite is limited due to its mostly massive and inconspicuous appearance. The most prized specimens are those that show even trace crystallization in the form of small, hexagonal crystals. Association with other, more aesthetic minerals from the Franklin deposit, such as willemite (fluorescent) or rhodochrosite, is also important. The purity and intensity of the brown color also affect the value of the specimen. ## Popular Localities By far the most sought-after specimens by collectors come from the type locality - the Trotter Mine in Franklin, New Jersey, USA. Material from this historic site is considered classic and serves as a reference point for this mineral.
Care and storage
## Cleaning Nelenite specimens should be cleaned very carefully, using a soft brush to remove dust. Brief use of distilled water is permissible, but prolonged soaking should be avoided. After wet cleaning, the specimen must be thoroughly dried. ## What to Avoid As an arsenosilicate, nelenite is potentially toxic if ingested or inhaled as dust, so situations leading to its pulverization should be avoided. It should be protected from contact with acids and other chemicals. It should not be subjected to ultrasonic cleaning or steam cleaning. Prolonged exposure to moisture can lead to its slow decomposition. ## Storage Nelenite specimens are best stored in closed, dry containers or display cases, away from direct sunlight and sources of moisture. It is recommended to include a label with a warning about arsenic content.