Hoganite

Chemical formula: Cu<sup>2+</sup>(CH<sub>3</sub>COO)<sup>1-</sup><sub>2</sub>·H<sub>2</sub>O

Hoganite is an extremely rare, blue organic mineral, a hydrated copper acetate, discovered in mine dumps in Australia.

## Characteristics Hoganite is a mineral from the acetate group, chemically known as hydrated copper(II) acetate. It forms prismatic, elongated crystals that can reach up to 2 mm in length. It usually occurs as single, well-formed crystals or small groups and aggregates thereof. Its intense blue color makes it visually distinctive, despite its small size. ## Physical Properties Hoganite crystals exhibit a vitreous luster. They are transparent to translucent. Due to its organic nature and small crystal size, many of its physical properties, such as hardness or density, have not been precisely determined. ## Colors and Varieties This mineral is characterized by a uniform, intensely blue color. No color varieties or commercial varieties are known. ## History and Name The name hoganite was given in honor of Graham P. Hogan

Properties

Mohs hardness
2
Luster
Vitreous
Streak
Light blue
Density
1.98
Cleavage
Perfect on {011}, less so on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features of hoganite are its intensely blue color, prismatic crystal habit, and specific, anthropogenic occurrence environment (mine dumps). Its water solubility is also an important, though destructive, identification feature. ## Distinguishing from Similar Minerals It can be confused with other secondary blue copper minerals, such as azurite or chalcanthite. It differs from azurite by its crystal habit (hoganite forms elongated prisms, azurite often forms tabular or massive aggregates). Distinguishing it from chalcanthite, which is also water-soluble, may require advanced analytical methods, although chalcanthite crystallizes in the triclinic system, and hoganite in the monoclinic system. ## Crystal Forms Hoganite forms well-developed, prismatic crystals, often elongated along one axis. They occur as single needles or in radial or chaotic aggregates.

Geological environment

## Genesis Hoganite is a secondary mineral, forming under anthropogenic conditions. Its formation is a result of chemical reactions occurring in the dumps of old copper mines. Acidic rainwater, flowing through rock material, reacts with decaying organic matter (e.g., wooden elements of old mining structures), leading to the formation of acetic acid. This acid then reacts with copper minerals, forming copper acetate crystals, i.e., hoganite, under favorable conditions. ## Mineral Associations At its discovery site, hoganite co-occurs with other rare, secondary copper minerals, such as paceite (calcium copper acetate), as well as gypsum, chalcanthite, malachite, and azurite. ## Localities The only confirmed locality of hoganite in the world is the Potosi mine in Broken Hill, New South Wales, Australia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria As an extremely rare mineral, every hoganite specimen is valuable to specialized collectors. Highly prized are specimens with well-formed, sharply terminated crystals of intense blue color and good transparency. The size of the crystals is also important – those exceeding 1 mm are already considered significant. Attractiveness is enhanced by a contrasting matrix or co-occurrence with other rare minerals, such as paceite. ## Popular Localities The only source of collector specimens is the type locality – the Potosi mine in Broken Hill, Australia. Material from this location is extremely limited and sought after by collectors of rare minerals and those specializing in minerals from this specific locality.

Care and storage

## Cleaning Due to their rarity and delicacy, hoganite specimens should be handled with the utmost care. Cleaning, if absolutely necessary, should be limited to very gentle brushing with a soft brush to remove loose dust. Any contact with water and chemicals should be avoided. ## What to Avoid As a water- and acid-soluble mineral, hoganite must be protected from moisture, water, water vapor, and all chemicals. It should also be protected from high temperatures and direct sunlight, which can lead to its dehydration and damage. ## Storage Specimens should be stored in a dry place, preferably in a sealed "perky box" to isolate them from changes in ambient humidity. Display should only take place under controlled conditions, away from sources of moisture and direct light.

Sources

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