Zaccariniite

Chemical formula: RhNiAs

Zaccarynite is an extremely rare nickel and rhodium arsenide, forming tiny, metallic inclusions in platinum-group element alloys.

## Characteristics Zaccarynite is a mineral with a metallic appearance, typically occurring as very small, rounded or irregular grains and inclusions within other minerals, mainly in platinum-group metal alloys. Its grains rarely exceed 100 micrometers in size. Observed in reflected light, it has a color ranging from grayish-white to creamy, with no visible pleochroism or anisotropy. ## Physical Properties Due to its extreme rarity and small grain size, most physical properties have not been precisely determined. Hardness is estimated at approximately 5 on the Mohs scale. The mineral is opaque and possesses a strong, metallic luster. The density calculated based on the chemical formula and unit cell parameters is 10.51 g/cm³. ## History and Name The mineral was named in honor of Federico Zaccarini, a professor of geology at the University of Leoben in Austria, in recognition of his contributions to the study of platinum-group minerals. It was approved by the International Mineralogical Association (IMA) in 2008 (IMA2008-069). The type locality from which it originates is Loma Peguera in the Dominican Republic.

Properties

Mohs hardness
3.5-4
Color
Grey
Luster
Metallic
Streak
Black
Density
10.09
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of zaccarynite is impossible without advanced analytical techniques. It requires analysis in reflected light using a polarizing microscope and chemical analysis using an electron microprobe (EDS/WDS) to confirm the composition (presence of rhodium, nickel, and arsenic in appropriate proportions). ## Distinguishing from similar minerals It can be confused with other small, metallic platinum-group minerals (PGM), such as gersdorffite, chloanthite, or other arsenides. Differentiation relies solely on precise chemical composition analysis. ## Crystal Forms It typically forms very small, irregular or rounded grains and inclusions. Well-formed crystals have not been observed.

Geological environment

## Genesis Zaccarynite forms under specific geological conditions, in ultramafic rocks (silica-poor) that have undergone serpentinization processes. It is a hydrothermal mineral, crystallizing at low temperatures from solutions rich in arsenic, nickel, and platinum-group metals. ## Mineral Associations It most commonly co-occurs with other platinum-group minerals, such as ruthenarsenite, irarsite, osarsite, as well as with chromite, awaruite, heazlewoodite, pentlandite, and chalcopyrite. ## Localities The main confirmed localities for this mineral are: - Loma Peguera in Monseñor Nouel Province, Dominican Republic (type locality). - Chromite deposits in the Othrys ophiolite massif in Greece. - Freetown intrusive complex in Sierra Leone. - Miessijoki River in Lapland, Finland.

Rarity

Extremely rare

For collectors

## Quality Criteria Zaccarynite is a mineral of purely scientific and reference importance. It does not form macroscopic specimens, and its collector value is negligible. In specialized collections, only properly documented and analyzed rock samples (so-called "polished sections") containing confirmed micro-inclusions of this mineral, originating from the type locality, are valued.

Care and storage

## Cleaning Due to the microscopic size of the grains and their occurrence as inclusions within the host rock, isolated cleaning of individual specimens is practically impossible and unnecessary. The host specimen can be gently cleaned with compressed air to remove dust. ## What to Avoid Avoid contact with strong acids and chemicals that could react with arsenic, nickel, or rhodium, as well as with surrounding minerals. Do not subject the specimen to ultrasound or sudden temperature changes. ## Storage Specimens containing zaccarynite should be stored under stable conditions, in closed containers or display cases, to protect them from dust and contaminants. Avoid humid environments.

External references

Sources

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