Selenolaurite

Chemical formula: RuSe<sub>2</sub>

Selenolaurite is an extremely rare ruthenium selenide with a metallic luster, occurring as microscopic, cubic crystals.

## Characteristics Selenolaurite is a very rare mineral from the sulfide group, being a ruthenium selenide. It occurs as extremely small, individual crystals with a regular, cubic habit, rarely exceeding 0.1 mm in size. Most often, it forms inclusions in other minerals, mainly in laurite. Due to its size, its observation requires significant magnification. It is opaque and black in color. ## Physical Properties This mineral is characterized by a metallic luster. Its Mohs hardness is high, at 6.5, which is a significant value for a representative of this group. The density is also high, which results from the presence of the heavy element, ruthenium. ## History and Name Selenolaurite was first described in 1992 by Z. Johan, M. Ohnenstetter, W. Fischer, and C. Amossé. Its name refers to its chemical composition – the dominance of selenium (seleno-) and its structural similarity to laurite, which is ruthenium sulfide (RuS₂). The mineral was approved by the International Mineralogical Association (IMA) under number IMA1991-029. The type locality, from which the first described samples originated, is the Hopei stream in the Madang region of Papua New Guinea.

Properties

Mohs hardness
6.5
Luster
Metallic
Streak
Black
Density
7.83
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Cubic

Diagnostic features

## Identification Identification of selenolaurite is possible only using advanced laboratory techniques, such as scanning electron microscopy (SEM) with chemical composition analysis (EDS/WDS). Visual properties, such as black color, metallic luster, and cubic crystal habit, are only indicative but do not allow for certain identification due to their microscopic size. ## Distinguishing from similar minerals Selenolaurite is practically impossible to distinguish with the naked eye from other opaque, metallic platinum-group minerals, such as laurite (RuS₂), irarsite (IrAsS), or osarsite (OsAsS), with which it often coexists. It differs from laurite by the dominance of selenium over sulfur, which can only be determined by chemical analysis. ## Crystal forms It forms euhedral, regular crystals with a cubic habit, reaching sizes up to 100 micrometers (0.1 mm).

Geological environment

## Genesis Selenolaurite is a mineral of magmatic origin. It forms in ultramafic ophiolite complexes, crystallizing from magma rich in platinum-group elements (PGE) and selenium. It forms at high temperatures as one of the early minerals crystallizing in the magma chamber. ## Mineral associations This mineral most often occurs as inclusions in laurite (RuS₂). It also coexists with other platinum-group minerals, such as irarsite, osarsite, as well as with chromite, osmium-iridium-ruthenium alloys (osiridium), and chalcopyrite. ## Localities Selenolaurite is an extremely rare mineral, identified so far in only a few locations worldwide. Besides the type locality in Papua New Guinea (Hopei stream, Madang), its presence has been confirmed in chromite deposits in the Othrys ophiolite complex in Greece and in nickel-copper deposits in Sudbury, Canada.

Rarity

Extremely rare

For collectors

## Quality criteria The collector's value of selenolaurite is purely scientific and systematic. Due to its microscopic size, specimens have no aesthetic appeal. The most valuable samples are those in which the presence of selenolaurite has been analytically confirmed, originating from the type locality or other well-documented occurrences. The richness of associations with other rare platinum-group minerals increases its value. ## Popular localities Specimens from the type locality in Papua New Guinea are most sought after by specialized scientific collections. Any specimen with analytically confirmed presence of this mineral, regardless of location, is considered an extremely valuable acquisition.

Care and storage

## Cleaning Due to the microscopic size of the crystals and their occurrence as inclusions in other minerals, cleaning individual selenolaurite specimens is practically impossible and not recommended. Any attempts at mechanical or chemical cleaning of the host rock can irreversibly destroy the delicate crystals. ## What to avoid Avoid using any chemicals, acids, or ultrasonic cleaning. Specimens containing selenolaurite should be protected from abrasion and mechanical damage. ## Storage Specimens with selenolaurite are best stored under stable conditions, in closed "micromount" boxes that protect them from dust, moisture, and physical damage. The label should precisely indicate the location of the microscopic crystals on the sample.

Sources

Read more