Ruthenarsenite

Chemical formula: (Ru,Ni)As

Ruthenarsenite is a rare ruthenium and nickel arsenide, occurring as fine, metallic grains in igneous rocks.

## Characteristics Ruthenarsenite is a rare mineral from the arsenide group, composed mainly of ruthenium and arsenic, with a frequent admixture of nickel. It forms very small, usually microscopic, anhedral (irregular) grains with a metallic luster. It typically occurs as inclusions within other ore minerals. Its color is gray to grayish-white, and on a fresh surface, it resembles steel. ## Physical Properties This mineral is characterized by high hardness, reaching 7 on the Mohs scale, and significant density, up to 9.3 g/cm³. It has a strong, metallic luster and is completely opaque. It exhibits no cleavage, and its fracture is uneven. The streak, which is the color of the powdered mineral, is black. ## Colors and Varieties Ruthenarsenite is uniform in color – it occurs in shades of gray. It does not form color varieties or commercial varieties. ## History and Name The mineral's name, given in 1974 by D.C. Harris, directly refers to its chemical composition – the elements ruthenium (Latin: *Ruthenia* – Rus') and arsenic. It was first identified in material from the Werner Lake area in the Kenora District, Ontario, Canada, which is its type locality. ## Uses Due to its extreme rarity and occurrence in the form of microscopic grains, ruthenarsenite has no industrial application. It is solely an object of scientific interest and is valued in specialized systematic collections.

Properties

Mohs hardness: 7
Luster: Metallic
Streak: Black
Density: 9.3
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification Identification of ruthenarsenite is impossible without advanced analytical techniques. Due to its microscopic size and occurrence in complex ore parageneses, it requires chemical composition analysis using an electron microprobe (EDS/WDS). Preliminary features, such as metallic luster, high hardness, and high density, can only suggest the presence of a platinum-group mineral. ## Distinguishing from Similar Minerals Ruthenarsenite is visually indistinguishable from many other platinum-group arsenides and sulfarsenides, such as irarsite, gersdorffite, hollingworthite, or sperrylite. Definitive differentiation is only possible based on chemical analysis. ## Crystal Forms This mineral almost always forms irregular, anhedral grains ranging in size from a few to several tens of micrometers. Grains with partially developed faces (subhedral) are rarely observed. It typically occurs as inclusions in sulfides (pentlandite, chalcopyrite) or in their vicinity.

Geological environment

## Genesis Ruthenarsenite is a mineral of magmatic origin. It forms in the late stages of crystallization within ultramafic and mafic magmatic intrusions, where sulfides and platinum-group elements (PGE) are concentrated. ## Mineral Associations It most commonly co-occurs with other ore minerals, such as pentlandite, chalcopyrite, pyrrhotite, as well as with other platinum-group minerals, including irarsite, gersdorffite, hollingworthite, and native gold. ## Localities The most important confirmed occurrences of this mineral worldwide include the type locality in the Werner Lake area in Canada, the Bushveld Igneous Complex in South Africa, intrusions in the Shetland Islands in the United Kingdom, and other nickel, copper, and platinum-group element deposits associated with ultramafic rocks.

Rarity

Very rare

For collectors

## Quality Criteria The quality of ruthenarsenite collector specimens is assessed solely from a scientific perspective. Since the mineral occurs as microscopic grains, its value is not based on aesthetics. The richness of grains in the studied sample, accurate analytical identification, and the presence of rare associated minerals are crucial. Specimens most often take the form of polished petrographic thin sections or small rock fragments in "micromount" boxes. ## Popular Localities The most valued research materials by specialized institutions and collectors come from the historical type locality in Canada (Werner Lake) and from the platinum-rich rocks of the Bushveld Complex in South Africa.

Care and storage

## Cleaning Ruthenarsenite specimens, due to their microscopic nature, generally do not require cleaning and should not be cleaned by amateur methods. If necessary, compressed air can be used to remove dust or a soft, dry brush. ## What to Avoid Contact of the mineral with acids and other aggressive chemicals should be avoided. Despite its hardness, it should be protected from impacts and abrasion, which could damage the fine grains or the surrounding rock matrix. ## Storage Store in stable conditions, in a dry place, preferably in a sealed "micromount" box, to protect the specimen from dust and mechanical damage.

Sources

IMA Mineral List (CNMNC)