Mcgovernite

Chemical formula: Zn₂+₃(Mn₂+,Mg,Fe₃+,Al)₄₂(As₃+O₃)₂(As₅+O₄)₄[(Si,As₅+)O₄]₈(OH)₄₂

Mcgovernite is a very rare arsenate and silicate of manganese, zinc, and magnesium, forming small, hexagonal, reddish-brown crystals.

## Characteristics Mcgovernite is a complex arsenate and silicate of manganese, zinc, and magnesium, belonging to the hematolite group. It occurs as small, tabular or pyramidal crystals with a hexagonal outline. It typically forms granular aggregates or occurs as inclusions in other minerals, mainly in calcite and willemite. Its size rarely exceeds a few millimeters. ## Physical Properties This mineral is characterized by a hardness of 4 on the Mohs scale. It has a vitreous to resinous luster. It is a relatively dense mineral, with a specific gravity of approximately 4.13 g/cm³. It exhibits perfect cleavage in one direction, parallel to the crystal base. ## Colors and Varieties Mcgovernite has a characteristic, deep reddish-brown color, sometimes transitioning into orange-red hues. No color varieties or commercial forms are known. ## History and Name The mineral was discovered in the Sterling Hill mine in Ogdensburg, Sussex County (New Jersey, USA). It was described by Charles Palache and L. H. Bauer in 1927. The name commemorates James J. McGovern (1869-1915), an American mineral collector whose collections formed the basis for many mineralogical studies of the Franklin region. ## Uses Mcgovernite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals from the Franklin-Sterling Hill locality.

Properties

Mohs hardness: 4
Luster: Vitreous to resinous
Streak: Reddish brown
Density: 4.13
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Mcgovernite can be identified by its characteristic reddish-brown color, hexagonal crystal habit (if visible), and perfect cleavage in one direction. Its occurrence in association with minerals from the Franklin deposit, such as willemite, franklinite, or calcite, is a key diagnostic clue. ## Differentiation from Similar Minerals It can be confused with other reddish-brown minerals from Franklin, such as some varieties of zincite or franklinite. However, zincite is usually more orange and has a different crystal habit. Franklinite is black, opaque, and has a metallic luster. Key features for distinguishing mcgovernite are its physical properties (hardness, cleavage) and, in laboratory conditions, chemical analysis. ## Crystal Forms Mcgovernite crystals are usually very small, with a tabular or pyramidal habit, and a distinct basal pinacoid. They often form granular or massive aggregates embedded in the host rock.

Geological environment

## Genesis Mcgovernite is a product of contact metamorphism of Precambrian, metamorphosed stratiform zinc, iron, and manganese ore deposits. It forms under complex geochemical conditions, in the presence of arsenic, within franklinite-willemite marbles (skarns). ## Mineral Associations This mineral co-occurs with a rich assemblage of minerals characteristic of the Franklin-Sterling Hill deposit. It is most often accompanied by calcite, willemite, franklinite, zincite, rhodochrosite, barite, as well as rarer arsenates such as magnussonite or holdenite. ## Localities The only confirmed and classic locality for mcgovernite in the world is the Sterling Hill mine in Ogdensburg, Franklin mining district, Sussex County, New Jersey, USA. This is its type locality.

Rarity

Very rare

For collectors

## Quality Criteria The most prized mcgovernite specimens are those with well-formed, eye-visible crystals of intense, reddish-brown color. Rich aggregates of the mineral on a contrasting background, for example, on white calcite, are also highly valued. Due to its rarity, any specimen with clearly identified mcgovernite is valuable for specialized collections. ## Popular Localities The only source of mcgovernite specimens is the historic Sterling Hill mine in New Jersey, USA. All samples available on the collector's market come from this single location, making them particularly sought after by collectors specializing in minerals from this unique locality.

Care and storage

## Cleaning Mcgovernite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its chemical composition (arsenic content) and possible reactivity, contact with water and any chemical agents should be avoided. If it is necessary to remove loose contaminants, compressed air can be used from a safe distance. ## What to Avoid Contact with acids and detergents, which can damage or chemically alter the mineral, must be strictly avoided. McGovernite is sensitive to high temperatures and humidity. It should not be cleaned in ultrasonic cleaners. Due to its arsenic content, avoid inhaling dust and wash hands after each contact with the specimen. ## Storage Mcgovernite specimens are best stored in stable, dry conditions, away from direct sunlight and heat sources. It is recommended to keep it in a closed, padded collector's box or display case to protect it from mechanical damage and dust. It is advisable to label the specimen with a warning due to its arsenic content.

Sources

IMA Mineral List (CNMNC)