Ferronigerite-6N6S

Chemical formula: (Al,Fe₃+,Zn₂+)₃(Al,Sn₄+,Fe₃+)₈O₁₅(OH)

Ferronigeryte-6N6S is a very rare, dark brown to black mineral from the nigerite group, occurring as small, hexagonal crystals in pegmatites.

## Characteristics Ferronigeryte-6N6S is a complex oxide of aluminum, iron, and tin, belonging to the nigerite group. It forms small, tabular crystals with a hexagonal outline, rarely exceeding a few millimeters in size. It typically occurs as individual crystals or small aggregates embedded in the host rock. ## Physical Properties This mineral is characterized by high hardness, ranging from 8 to 9 on the Mohs scale, making it one of the harder minerals. It has a strong, almost metallic or metallic luster. It is opaque. The density ranges from 4.52 to 4.65 g/cm³. ## Colors and Varieties Ferronigeryte-6N6S is dark brown to black, sometimes with a reddish tint. The streak is reddish-brown. No distinct color varieties or commercial varieties are recognized. ## History and Name The name "ferronigeryte" refers to its chemical composition – the dominance of iron (Latin: *ferrum*) – and its relation to the structurally similar nigerite. The "-6N6S" suffix is a designation for a specific polytype within the ferronigeryte subgroup. The mineral was described and approved by the International Mineralogical Association (IMA) as a distinct mineral species.

Properties

Mohs hardness: 8-9
Luster: Submetallic to metallic
Streak: Reddish-brown
Density: 4.52-4.65
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features include the hexagonal outline of crystals, black or dark brown color, high hardness (8-9 on the Mohs scale), and a reddish-brown streak. Its occurrence in granitic pegmatites is also an important clue. ## Distinguishing from Similar Minerals It can be confused with other black, hard oxide minerals found in pegmatites, such as Magnetite, Ilmenite, Spinel (Hercynite), or Tourmaline (Schorl). It differs from Magnetite by its lack of magnetism. From Schorl, it differs in crystal form (hexagonal tablets vs. trigonal columns with a characteristic cross-section) and the absence of striations on the prism faces. Final distinction from other minerals of the nigerite or spinel groups requires advanced analytical methods (e.g., EDS, XRD). ## Crystal Forms It forms thin to thick tabular crystals with a hexagonal outline. Crystals are usually small, up to several millimeters in diameter.

Geological environment

## Genesis Ferronigeryte-6N6S is a pegmatitic mineral. It forms in granitic pegmatites, rich in lithium and phosphates, as a product of crystallization in the late stages of their formation. ## Mineral Associations It co-occurs with minerals such as Quartz, Microcline, Albite, Muscovite, as well as lithium minerals (Spodumene, Lepidolite, Amblygonite) and other oxides like Cassiterite and Columbite-Tantalite. ## Localities The most important and best-documented locality for this mineral in the world is the pegmatite in the area of Nová Ves, near Český Krumlov in southern Czechia. This is its type locality (the place of its first discovery and description).

Rarity

Very rare

For collectors

## Quality Criteria The quality of a Ferronigeryte-6N6S specimen is primarily assessed based on the development and size of its crystals. Sharp, well-defined, undamaged hexagonal crystals that stand out clearly from the host rock (matrix) are most highly valued. Luster and the absence of mechanical damage also increase the specimen's value. ## Popular Localities The only source of collectible specimens of this mineral is its type locality in Czechia (Nová Ves near Český Krumlov). Specimens from this location are highly sought after by collectors specializing in mineral systematics and rare minerals.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to its rarity and potential fragility, ultrasonic cleaners and aggressive methods should be avoided. ## What to Avoid Contact with acids and strong chemicals, which could potentially damage the mineral's surface, should be avoided. Despite its high hardness, specimens can be brittle, so they should be protected from impacts and falls. ## Storage It is recommended to store specimens in separate, padded display boxes to prevent scratching by other minerals (although it is very hard itself) and mechanical damage. It should be protected from dust and contaminants.

Ferronigerite-6<i>N</i>6<i>S</i>