Plumbojohntomaite

Chemical formula: Pb<sup>2+</sup>Fe<sup>2+</sup><sub>2</sub>Fe<sup>3+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>(OH)<sub>3</sub>

Plumbojohntomaite is a rare phosphate mineral of the bjarebyite group, distinguished by the presence of lead and iron, and occurring as small, dark crystals.

## Characteristics Plumbojohntomaite is a complex hydrated lead iron phosphate belonging to the bjarebyite group. It forms very small, tabular or lath-like crystals, rarely exceeding 0.5 mm in length. They usually occur as radial or tangled aggregates. It is a dark-colored mineral with a vitreous luster. ## Physical properties Plumbojohntomaite crystals are brittle. The mineral has a hardness of approximately 4 on the Mohs scale and a density of 4.45 g/cm³. It has a vitreous luster and is translucent to opaque. The streak is greenish-gray. ## Colors and varieties Plumbojohntomaite occurs in dark green to black colors. No varieties have been distinguished. ## History and name The mineral's name refers to its chemical composition – "plumbo" from the Latin word *plumbum* meaning lead, and to its relation to johntomaite, another mineral from the same group. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2006 (number 2006-031). It was described by Ian E. Grey and co-workers in 2007 based on material from the Spring Creek mine in South Australia.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
Greenish grey
Density
4.45
Cleavage
Good on {001}
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Amateur identification of plumbojohntomaite is practically impossible due to the microscopic size of its crystals and its similarity to other secondary minerals. Definitive identification requires advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). ## Distinguishing from similar minerals Plumbojohntomaite is visually indistinguishable from other minerals of the bjarebyite group, such as johntomaite, bjarebyite, or plumboperloffite. They differ in the proportions of elements (lead, barium, strontium, manganese, iron), which can only be determined by chemical analysis. ## Crystal forms The mineral forms very small, tabular or lath-like crystals, often flattened parallel to {001}. These crystals combine into radial or haphazardly tangled aggregates, forming small clusters on the surface of the host rock.

Geological environment

## Genesis Plumbojohntomaite is a secondary mineral that crystallizes in the late stages of hydrothermal processes or in the oxidation zones of ore deposits. It forms as a result of the alteration of primary minerals containing phosphorus and lead in an iron-rich environment. ## Mineral associations This mineral co-occurs with other secondary phosphates. At its type locality (Spring Creek mine, Australia), it was found in association with rockbridgeite, strengite, cyrilovite, cacoxenite, apatite-(CaF), as well as goethite and quartz. ## Localities Confirmed occurrences of plumbojohntomaite are very few. The most important locality, which is also the discovery site (type locality), is the Spring Creek copper mine in the Flinders Ranges, South Australia. Another known locality is the Silver Bill mine in Arizona, USA.

Rarity

Very rare

For collectors

## Quality criteria As a micromineral, plumbojohntomaite is valued primarily for the richness and development of crystals within an aggregate. The most desirable specimens are those with clearly formed, radial clusters of dark green crystals, contrasting with the lighter host rock. Association with other rare phosphates is also important. ## Popular localities By far the most valued and commonly encountered specimens in collections come from the type locality – the Spring Creek mine in South Australia.

Care and storage

## Cleaning Due to the small size and brittleness of the crystals, mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Contact with water, especially with chemicals, is not advised. ## What to avoid Avoid contact with acids and other aggressive chemicals that can damage the mineral. The crystals are brittle and susceptible to mechanical damage, so vibrations, impacts, and abrasion should be avoided. It should not be heated. ## Storage Plumbojohntomaite specimens, as microminerals, are best stored in specialized "micromount" boxes that protect them from dust and mechanical damage. Display should be away from sources of vibration and direct sunlight.

Sources

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