Johnbaumite-M

Chemical formula: Ca₅(AsO₄)₃OH

Johnbaumite-M is a rare calcium arsenate from the apatite group, forming colorless to white, hexagonal crystals.

## Characteristics Johnbaumite-M is a mineral belonging to the apatite group, being the arsenate analog of hydroxylapatite. It typically occurs as small, hexagonal, prismatic crystals, which can be elongated or short and tabular. It also forms granular and massive aggregates. It is colorless, white, or grayish, and its crystals can be transparent to translucent. ## Physical Properties This mineral is characterized by a hardness of 5 on the Mohs scale, which is typical for minerals of the apatite group. It has a vitreous to resinous luster. The density of johnbaumite-M is approximately 3.73 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## History and Name Johnbaumite-M was named in honor of John L. Baum (1916-2011), an American mineral collector and curator from Franklin, New Jersey, who first noticed this mineral. Originally described as johnbaumite in 1980, its name was modified in 2010 to johnbaumite-M in connection with the revision of the apatite group nomenclature, where the suffix "-M" indicates its monoclinic crystal symmetry. ## Uses Johnbaumite-M has no industrial significance. It is solely a mineral of scientific and collecting importance, sought after for its rarity and association with the classic Franklin locality in the USA.

Properties

Mohs hardness: 5
Luster: Vitreous to resinous
Streak: White
Density: 3.73
Cleavage: Indistinct on {0001}
Fracture: Conchoidal to uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Johnbaumite-M is most often identified by its characteristic hexagonal crystal form, typical of the apatite group. Its occurrence in the specific geological environment of the Franklin and Sterling Hill deposits, in association with other rare minerals, is a key indicator. However, confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Differentiation from Similar Minerals It can be confused with other minerals from the apatite group, especially mimetite and hydroxylapatite. It is distinguished from hydroxylapatite by the dominance of arsenic over phosphorus. Mimetite is often yellow or orange, while johnbaumite-M is usually colorless or white. Final differentiation requires chemical analysis. ## Crystal Forms Crystals are typically hexagonal (in outline), prismatic, terminated by flat basal faces or pyramids. It also occurs in the form of granular aggregates, radial aggregates, or as massive fillings.

Geological environment

## Genesis Johnbaumite-M is a mineral of metamorphic origin. It forms in zinc, iron, and manganese ore deposits that have undergone contact metamorphism and metasomatism. It occurs in calcite veins cutting skarns and ore deposits. ## Mineral Associations This mineral co-occurs with many other, often rare minerals, characteristic of the Franklin and Sterling Hill localities. The most common associations include: andradite, franklinite, willemite, zincite, calcite, barite, as well as other arsenates like allactite or magnussonite. ## Localities The most important and classic localities, from which most known specimens originate, are the Franklin and Sterling Hill mines in Sussex County, New Jersey, USA. These are the only places in the world where johnbaumite-M occurs in well-formed, collectible specimens.

Rarity

Very rare

For collectors

## Quality Criteria The most prized johnbaumite-M specimens are those with sharply terminated, well-formed, transparent crystals with a distinct luster. Crystals embedded in a contrasting matrix, for example with franklinite or willemite, are particularly sought after. Crystal size is also an important factor – specimens with crystals exceeding several millimeters are considered exceptional. ## Popular Localities By far the most valued and known specimens come from the Franklin mine in New Jersey, USA. This is the type locality for this mineral and the source of practically all specimens available on the collector's market.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Distilled water is permissible, but prolonged soaking should be avoided. After wet cleaning, the specimen must be thoroughly dried. ## What to Avoid Contact with acids, which can quickly damage or dissolve the mineral, should be strictly avoided. Johnbaumite-M is relatively soft and brittle, so it must be protected from impacts and scratches. It should not be heated or subjected to ultrasound. ## Storage Specimens are best stored in individual, padded collector boxes to avoid contact with harder minerals. They should be protected from dust and moisture. Exposure to strong light is not harmful, but storage in stable room conditions is recommended.

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