Andrieslombaardite

Chemical formula: Rh<sup>3+</sup>(SbS)<sup>3-</sup>

Andrieslombaardite is an extremely rare rhodium antimony sulfide, forming microscopic, metallic inclusions in platinum-group element alloys.

## Characteristics Andrieslombaardite is a rhodium antimony sulfide belonging to the irarsite group. It occurs as extremely small, rounded or irregular grains, usually not exceeding 60 micrometers in size. It most often forms complex intergrowths with other platinum-group minerals (PGM), such as irarsite, laurite, or native platinum. It is opaque and has a metallic luster. ## Physical Properties Due to the microscopic size of its crystals, most physical properties, such as hardness, density, cleavage, or fracture, have not been precisely determined. Hardness is estimated based on VHN (Vickers) hardness, which is 1016 kg/mm², suggesting high hardness on the Mohs scale, likely above 7. Density has also not been measured, but only calculated based on the formula and unit cell parameters, and is 8.31 g/cm³. ## Colors and Varieties The mineral has a gray color with a slight bluish tint in reflected light. No varieties have been distinguished. ## History and Name Andrieslombaardite was discovered in platinum-bearing concentrates from the Witwatersrand River in the Republic of South Africa. It was described and approved as a new mineral by the International Mineralogical Association (IMA) in 2003 (IMA2003-045). The name honors Dr. Andries F. Lombaard (born 1928), a South African geologist who made significant contributions to the study of the geology of the Bushveld Complex, one of the world's most important sources of platinum-group metals. ## Uses Andrieslombaardite has no industrial application. Its significance is purely scientific and collectible, as an extremely rare member of the platinum-group metal sulfide group.

Properties

Mohs hardness
7
Luster
Metallic
Streak
Black
Density
8.31
Cleavage
None
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Identification of andrieslombaardite is possible only with advanced laboratory techniques. Under a reflected light ore microscope, it has a characteristic gray color with a bluish tint. Final confirmation requires chemical composition analysis by X-ray microanalysis (EDS/WDS) and X-ray diffraction (XRD) studies to determine the crystal structure. ## Distinguishing from Similar Minerals Andrieslombaardite is visually almost impossible to distinguish from other platinum-group sulfides and arsenosulfides, such as irarsite, hollingworthite, ruarsite, or osarsite, with which it often co-occurs. Differences can only be determined by precise chemical analysis, which will show a dominance of rhodium and antimony with an absence or trace amounts of arsenic, iridium, ruthenium, or osmium. ## Crystal Forms This mineral forms very small, rounded or irregular grains up to 60 micrometers in size. No well-formed, idiomorphic crystals have been observed.

Geological environment

## Genesis Andrieslombaardite is a magmatic mineral, crystallizing in the late stages of processes occurring in ultramafic and mafic magmatic intrusions. It forms in sulfide deposits rich in platinum-group elements (PGE), where it crystallizes from residual sulfide melts. ## Mineral Associations This mineral occurs in close association with other platinum-group minerals (PGM). It is most often accompanied by irarsite, laurite, hollingworthite, platarsite, sperrylite, native platinum, as well as chalcopyrite, pentlandite, and pyrrhotite. ## Localities The only confirmed occurrence of andrieslombaardite in the world (type locality) is in heavy mineral concentrates from the Witwatersrand River in Gauteng Province, Republic of South Africa. This material was obtained from river sediments eroding rocks of the Bushveld Igneous Complex.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of an andrieslombaardite specimen is assessed solely in a scientific and micromount context. Since the mineral occurs as microscopic grains, its value depends on the size of the inclusion, its purity (lack of intergrowths with other minerals), and the quality of the analysis confirming its identification. These specimens are not available in commercial trade and are mainly found in the collections of research institutions. The most valuable are polished sections where the andrieslombaardite grain is clearly visible and well-separated from the surrounding minerals. ## Popular Localities The only source of this mineral is its type locality in the Republic of South Africa, associated with the Bushveld Complex.

Care and storage

## Cleaning Andrieslombaardite specimens occur as microscopic inclusions in polished rock samples or metal alloys. Cleaning is usually neither necessary nor possible under amateur conditions. If needed, the polished surface can be wiped with a very soft, dry microfiber cloth to remove dust or fingerprints. ## What to Avoid Avoid contact with any chemicals, acids, and abrasive agents that could damage both the mineral itself and the surrounding rock or metallic matrix. Ultrasonic cleaners should not be used. Specimens should be protected from scratching. ## Storage Specimens containing andrieslombaardite are best stored in specialized mineral boxes (so-called micromounts) that protect them from dust, moisture, and mechanical damage. Avoid exposure to extreme temperatures and humid environments.

Sources

Read more