Janggunite

Chemical formula: (Mn⁴⁺,Mn²⁺,Fe³⁺)₆O₈(OH)₆

Janggunite is a rare manganese and iron oxyhydroxide, forming aggregates of fibrous or bladed crystals with a metallic luster.

## Characteristics Janggunite is a rare mineral from the oxide group, chemically classified as a manganese and iron oxyhydroxide. It occurs as aggregates of small, bladed or fibrous crystals, which can form rosetted or radial aggregates. Its appearance is characteristic – it typically forms massive, earthy, or fibrous aggregates in rock fissures and cavities. Individual crystals are very small, rarely exceeding a few millimeters in length. ## Physical Properties This mineral is relatively soft, with a Mohs hardness ranging from 2 to 3. It is opaque and characterized by a metallic or submetallic luster. The density of janggunite ranges from 3.55 to 3.61 g/cm³. It is brittle, and its crystals are easily damaged. ## Colors and Varieties Janggunite is dark brown to black in color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from the Janggun Mine in Gyeongsangbuk-do, South Korea, where it was discovered and first described in 1975 by Kim Soo Jin. This is its type locality. ## Uses Janggunite has no industrial application. It is solely a mineral of scientific and collector's interest, sought after for its rarity and origin.

Properties

Mohs hardness: 2-3
Color: black
Luster: Metallic
Streak: brownish black to dark brown
Density: 3.59
Cleavage: one direction
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Janggunite can be identified by its characteristic mode of occurrence – it forms radial, fibrous, or bladed aggregates of dark brown to black color with a metallic luster. Its low hardness and reddish-brown streak are also diagnostic features. It occurs in the oxidation zones of manganese deposits. ## Distinguishing from Similar Minerals Janggunite is sometimes confused with other manganese oxides, such as pyrolusite, hollandite, or todorokite. It differs from pyrolusite by its reddish-brown streak (pyrolusite has a black streak) and typically more fibrous form. Distinguishing it from todorokite and other rare manganese oxides often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Janggunite crystals are very small, bladed or acicular, elongated along one axis. They typically form radial, stellate, or fibrous aggregates, as well as earthy and massive masses.

Geological environment

## Genesis Janggunite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal manganese deposits. It forms as a result of the alteration of earlier manganese minerals under low-temperature and low-pressure conditions, with access to atmospheric oxygen. ## Mineral Associations This mineral co-occurs with other manganese oxides and hydroxides, such as todorokite, birnessite, pyrolusite, cryptomelane, as well as with calcite, kutnohorite, and goethite. ## Localities The most important and type locality for janggunite is the Janggun Mine in South Korea. It is also known from several other localities worldwide, including the Ōmori Mine in Iwate Prefecture, Japan, and the Silver Monument Mine in Grant County, New Mexico, USA.

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, radial aggregates of fibrous or bladed crystals, clearly contrasting with the host rock. The aesthetic composition and the absence of damage to the delicate needles are important. Specimens from the type locality (Janggun Mine) are particularly sought after. ## Popular Localities By far the most desirable specimens come from the Janggun Mine in South Korea. Good quality collector's material also comes from Japan (Ōmori Mine).

Care and storage

## Cleaning Janggunite specimens are very delicate and brittle. They should only be cleaned dry with a soft brush to remove dust. The use of water, especially ultrasonic cleaners, is highly inadvisable and can lead to the disintegration of aggregates. ## What to Avoid Avoid contact with water, acids, and other chemicals. The brittle aggregates are sensitive to shocks, impacts, and abrasion. Do not expose specimens to high temperatures. ## Storage It is recommended to store janggunite specimens in sealed display boxes, away from dust and moisture. Due to its brittleness, it should be isolated from harder minerals to prevent scratches and mechanical damage.