Laurite

Chemical formula: Ru²⁺(S₂)²⁻

Laurite is a rare ruthenium sulfide, valued by collectors for its well-formed, metallic-lustered, isometric crystals.

## Characteristics Laurite is a ruthenium sulfide belonging to the pyrite group. It forms small, but usually well-formed, octahedral or cubo-octahedral crystals. Less commonly, it occurs as granular aggregates or as inclusions in other minerals, mainly in platinum and chromite. Its most characteristic features are a strong, metallic luster and high density. Specimens are typically very small, rarely exceeding a few millimeters, but their ideal, geometric forms make them desirable collector's items. ## Physical Properties Laurite is a very hard and dense mineral. Its Mohs hardness is 7.5, making it resistant to scratching. The density is significant, reaching 6.43 g/cm³, which is noticeable even in small crystals. It is brittle and has an uneven to conchoidal fracture. It does not exhibit cleavage. It is opaque. ## Colors and Varieties This mineral is iron-black to black, with a strong metallic luster. It sometimes contains admixtures of osmium, iridium, rhodium, and iron, which may slightly affect its properties but do not form distinct, named varieties. ## History and Name Laurite was first described in 1866 by Friedrich Wöhler. The name comes from Laura, the wife of Charles A. Joy, an American chemist who provided Wöhler with the first samples for study. The type material originated from Borneo, Indonesia, where laurite occurred in platinum-bearing streams. ## Uses Due to its rarity and small crystal size, laurite has no industrial applications. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 7-7.5
Color: Black
Luster: Metallic
Streak: Dark grey
Density: 6.43
Cleavage: {111}
Fracture: Sub-Conchoidal
Transparency: Opaque
Crystal system: Isometric

Diagnostic features

## Identification Laurite is primarily identified by its characteristic, isometric crystal form (octahedra), very high hardness (7.5 on the Mohs scale), black color, and strong metallic luster. Its high density is also an important diagnostic feature. It occurs in a specific geological environment, which aids identification. ## Distinguishing from Similar Minerals Laurite can be confused with other black, metallic minerals. It is distinguished from magnetite by its lack of magnetism and higher hardness. It is distinguished from chromite by its crystal form (chromite rarely forms such perfect octahedra) and significantly higher hardness. It is distinguished from pyrite, to which it is related, by its color (pyrite is brass-yellow) and much greater rarity of occurrence. ## Crystal Forms Laurite crystals almost always take the form of regular octahedra {111}, sometimes with small cube faces {100}. They occur as single, overgrown crystals or inclusions in other minerals. Granular aggregates are less common.

Geological environment

## Genesis Laurite crystallizes in ultramafic igneous complexes, in rocks such as dunites and chromitites. It forms at high temperatures as a result of magmatic segregation. It is also found secondarily in placer deposits (alluvium), where it accumulates due to its high density and resistance to weathering. ## Mineral Associations This mineral most commonly co-occurs with platinum-group minerals (PGM), such as native platinum, osmiridium, iridosmine, as well as with chromite, cooperite, braggite, and sperrylite. ## Localities The most important historical locality is Borneo, Indonesia. Other significant localities include the Bushveld Complex in South Africa (Onverwacht, Mooihoek mines), the Stillwater Complex in Montana (USA), the Urals in Russia, as well as some deposits in Colombia, Ethiopia, and Greece.

Rarity

Rare

For collectors

## Quality Criteria The most prized laurite specimens are those with sharp, well-formed, undamaged crystals with a strong metallic luster. Ideal octahedra, especially those exceeding 2-3 mm in size, are considered exceptional. The attractiveness is also enhanced by the contrasting placement of a black crystal on a light rock matrix, although most specimens are isolated crystals recovered from alluvium. ## Popular Localities Specimens from the historical localities in Borneo are considered classic and most desirable. High-quality crystals also come from the Bushveld Complex in South Africa, which is currently the main source of this mineral on the collector's market.

Care and storage

## Cleaning Laurite specimens should be cleaned very carefully, preferably using compressed air to remove dust. If wet cleaning is necessary, it is recommended to use a soft brush and distilled water, then thoroughly dry the specimen. ## What to Avoid Avoid contact with acids and strong chemicals, which can damage the crystal surface. Despite its high hardness, the mineral is brittle, so it should be protected from impacts and falls. It should not be heated or cleaned with ultrasonics. ## Storage Collector's specimens of laurite, due to their small size, are best stored in enclosed "micromount" boxes, which protect them from dust and mechanical damage. It does not require special conditions regarding light or humidity.