Ferrihollandite

Chemical formula: Ba(Mn₄+₆Fe₃+₂)O₁₆

Ferrihollandite is a rare oxide from the hollandite group, distinguished by its black color, metallic luster, and occurrence in radial aggregates.

## Characteristics Ferrihollandite is a mineral from the hollandite group, belonging to the oxide class. Chemically, it is a barium, manganese, and iron oxide. It forms acicular or prismatic crystals, which most commonly occur as radial or fibrous aggregates. Less frequently, it is found in granular masses or earthy forms. Its characteristic features are its black, opaque color and strong, metallic luster. ## Physical Properties Ferrihollandite is characterized by relatively high hardness, approximately 6 on the Mohs scale. It has a metallic to submetallic luster. It is an opaque mineral with a high density, ranging from 4.84 to 5.13 g/cm³. The streak left on a streak plate is black. ## Colors and Varieties This mineral is monochromatic – it occurs exclusively in black. No color or commercial varieties are distinguished. ## History and Name The name "ferrihollandite" refers to its chemical composition – the dominance of iron (Latin: *ferrum*) and its structural relationship with hollandite, another mineral from the same group. It was formally described and recognized as a new mineral species by the International Mineralogical Association (IMA) in 1999. The type locality, from which the first described specimens originated, is the Kajlidongri mine in Jhabua district, Madhya Pradesh state, India.

Properties

Mohs hardness: 6
Luster: Metallic to submetallic
Streak: Black
Density: 4.84 - 5.13
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Ferrihollandite can be identified by its black color, strong metallic luster, and characteristic forms of occurrence – most often radial or fibrous aggregates. A black streak and relatively high hardness are also important diagnostic features. ## Distinguishing from Similar Minerals It can be confused with other black manganese oxides, such as hollandite, cryptomelane, or pyrolusite. It differs from hollandite by the dominance of iron over aluminum and titanium, which requires chemical analysis. It is harder than pyrolusite (pyrolusite has a hardness of 2-6 and often soils fingers). Cryptomelane has very similar properties, and often the only way to definitively distinguish them is by X-ray diffraction (XRD) or chemical analysis. ## Crystal Forms Crystals are monoclinic, prismatic or acicular in habit, often elongated. They typically form radial, stellate, or fibrous aggregates. They also occur in granular and botryoidal masses.

Geological environment

## Genesis Ferrihollandite is a mineral formed as a result of metamorphic processes. It forms in manganese-rich sedimentary rocks that have undergone regional metamorphism, typically under greenschist facies conditions. It can also form in the oxidation zones of manganese deposits. ## Mineral Associations It most commonly co-occurs with other manganese minerals, such as braunite, birnessite, piemontite, as well as with quartz, hematite, and mica. ## Localities The most important and classic locality, which is the type locality, is the Kajlidongri mine in Madhya Pradesh, India. This mineral has also been identified in several other locations worldwide, including the Kombat mine in Namibia and the Långban region in Sweden, known for its rare manganese minerals.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, radial aggregates of acicular crystals, forming striking "suns" or "stars" on the rock matrix. The size of the aggregates, their completeness, and intense, metallic luster are also important. Contrast with a light matrix rock (e.g., quartz) enhances the visual appeal of the specimen. ## Popular Localities By far the most known and valued specimens come from the type locality – the Kajlidongri mine in India. Specimens from this locality are considered exemplary for this mineral.

Care and storage

## Cleaning Ferrihollandite specimens can be cleaned with a soft, dry brush to remove dust. For heavier soiling, distilled water may be used. Ultrasonic cleaners should be avoided, as they can damage delicate, acicular crystals. ## What to Avoid The mineral is sensitive to strong acids, which can damage it. It should be protected from impacts and scratching, despite its relatively high hardness. Prolonged exposure to moisture is not advisable. ## Storage It is recommended to store specimens in closed boxes or display cases to protect them from dust and mechanical damage. Particularly fragile, acicular aggregates require careful handling and a stable base.

Sources

IMA Mineral List (CNMNC)