Manganosite

Chemical formula: Mn²⁺O

Manganite is a rare manganese oxide that quickly develops a black patina in air, while its fresh surfaces exhibit a characteristic emerald-green color.

## Characteristics Manganite is a manganese(II) oxide and the mineralogical analogue of periclase. Its most characteristic feature is an intense, emerald-green to grass-green color on fresh fracture surfaces. However, this mineral is unstable under oxygenic conditions and oxidizes very quickly, becoming covered with a black, dull layer of higher-order oxides, such as hausmannite or pyrolusite. For this reason, green, unaltered fragments are rarely visible and are usually surrounded by a black, opaque mass. It occurs in granular or massive aggregates, and well-formed crystals are extremely rare. ## Physical Properties This mineral is characterized by a hardness ranging from 5.5-6 on the Mohs scale and a significant density of approximately 5.4 g/cm³. It possesses perfect cleavage in three directions, causing it to break into cubic or prismatic fragments. The luster on fresh surfaces is vitreous, but it quickly becomes dull due to oxidation. ## Colors and Varieties The dominant and sole color of fresh manganite is emerald-green. Any other colors, mainly shades of brown and black, are a result of its surface alteration. No color varieties or commercial types of this mineral are distinguished. ## History and Name The name manganite, given in 1817 by the German mineralogist Carl Friedrich Jasche, directly refers to its chemical composition – a high manganese content (German: *Mangan*). The mineral was known earlier, but it was formally described only then. ## Uses Due to its rarity and instability, manganite has no industrial applications. It is solely an object of interest for collectors of rare minerals and scientific institutions.

Properties

Mohs hardness: 5.5
Color: Emerald-green, darkening on exposure to black
Luster: Vitreous
Streak: Brown
Density: 5.364
Cleavage: {001}
Fracture: Conchoidal,Sub-Conchoidal
Transparency: Transparent,Translucent
Crystal system: Isometric

Diagnostic features

## Identification A key diagnostic feature is the emerald-green color visible on a fresh fracture, which contrasts with the black, dull alteration crust. A green streak is also very characteristic. Perfect, cubic cleavage is helpful in identification, if visible. ## Distinguishing from Similar Minerals Green manganite is sometimes confused with other green secondary minerals from oxidation zones, such as malachite or annabergite. Manganite differs from them by its significantly greater hardness and density, as well as its characteristic green streak. Malachite additionally effervesces with hydrochloric acid, and annabergite forms different types of aggregates. The black, altered form is visually indistinguishable from other manganese oxides (pyrolusite, hausmannite) and requires chemical analysis or observation of a fresh fracture.

Geological environment

## Genesis Manganite is a mineral formed under reducing conditions, in manganese-rich metamorphic rocks or in metasomatic deposits. It forms during contact and regional metamorphism of manganese ore deposits, often as a result of the reduction of higher manganese oxides at high temperatures. ## Mineral Associations It often co-occurs with other manganese minerals, such as rhodonite, rhodochrosite, hausmannite, tephroite, as well as franklinite, willemite, and zincite (in the Franklin deposit). It also occurs in association with calcite and barite. ## Localities The most important and classic localities for this mineral are Långban and Nordmark in Sweden, and the Franklin and Sterling Hill deposits in New Jersey, USA, where the best specimens were found. It also occurs in Broken Hill, Australia, and in several locations in South Africa (e.g., Wessels Mine).

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with the largest possible, intensely green, unaltered surface of manganite. The contrast between the emerald color and the black, altered mass is highly desired. Well-formed, even small, cubic crystals are extremely rare and command very high prices. The size of the specimen is less important than the quality and surface area of the preserved green mineral. ## Popular Localities Specimens from the historic localities of Franklin, New Jersey (USA) and Långban (Sweden) are considered the best in the world. Most of the classic, rich specimens found in old museum and private collections originate from these places.

Care and storage

## Cleaning Manganite specimens are generally not cleaned. Any attempt to remove the black oxide patina (e.g., mechanically or chemically) can destroy the delicate, green layer underneath. Contact with water and chemicals should be avoided. ## What to Avoid The greatest threat to manganite is atmospheric oxygen and moisture, which cause its irreversible darkening. It is absolutely essential to avoid humid environments, direct sunlight, and high temperatures, which can accelerate the oxidation process. No acids or other cleaning agents should be used. ## Storage Manganite specimens require special storage conditions. They are best kept in sealed, colorless "perky box" containers away from sources of light and moisture. Advanced collectors store it in an oxygen-free atmosphere (e.g., in nitrogen) or in special mineral oils to slow down the oxidation process.