Orcelite

Chemical formula: Ni₄.₇₅As₂

Orcelite is a rare nickel arsenide, forming microscopic, hexagonal crystals with a metallic luster and a brownish-red or pinkish hue.

## Characteristics Orcelite is a nickel arsenide, typically occurring as very fine, hexagonal grains or plates, rarely exceeding 0.1 mm. It most often forms inclusions in other minerals, mainly in serpentinites and chromitites. Its metallic luster and characteristic brownish-red color with a pinkish hue are its main visual features. Due to the small size of the crystals, its identification requires specialized equipment. ## Physical properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. It has a high, metallic luster and is opaque. Its density is significant, around 7.6 g/cm³. It does not exhibit cleavage, and its fracture is uneven. ## Colors and varieties Orcelite has a fairly consistent coloration. It is observed in brownish-red shades, often with a distinct pinkish or purplish tone. In reflected light under a microscope, its color is described as creamy-pink. No varieties have been distinguished. ## History and name The mineral's name comes from the Col d'Orcel pass in France, where it was first found and described in 1959 by Simone Caillère, Jacques Avias, and Jean Falgueirettes. It was approved by the International Mineralogical Association (IMA) in the same year. ## Uses Orcelite has no industrial applications. Its significance is purely scientific and collectible, as a rare component of certain ultramafic rocks.

Properties

Mohs hardness: 5
Color: Rose-bronze
Luster: Metallic
Streak: Black
Density: 6.5
Cleavage: None
Fracture: Uneven
Transparency: Opaque
Crystal system: Hexagonal

Diagnostic features

## Identification Amateur identification of orcelite is practically impossible due to the microscopic size of its grains. It requires advanced laboratory methods, such as chemical composition analysis (EDS) with an electron microscope and X-ray diffraction (XRD) analysis. In reflected light under an ore microscope, it can be recognized by its characteristic creamy-pink color and anisotropy. ## Distinguishing from similar minerals It can be confused with other nickel arsenides, such as maucherite or nickeline. Nickeline has a similar color but usually forms larger aggregates. Maucherite has a different chemical composition and crystallizes in the tetragonal system. Definitive differentiation requires laboratory analysis. ## Crystal forms Orcelite forms small, hexagonal crystals with a tabular or platy habit. They usually occur as dispersed, single grains or small clusters within the host rock.

Geological environment

## Genesis Orcelite is a low-temperature hydrothermal mineral. It forms during the serpentinization of ultramafic rocks, such as peridotites and dunites. It develops in nickel- and arsenic-rich environments, often in the presence of sulfides. ## Mineral associations It most commonly co-occurs with minerals from the serpentine group (antigorite, lizardite), chromite, magnetite, pentlandite, heazlewoodite, awaruite, maucherite, nickeline, chalcopyrite, and bornite. ## Localities The most important occurrences of orcelite worldwide include the type locality in Tiébaghi, New Caledonia (an overseas territory of France), from which the best-formed specimens originate. It is also known from the Bushveld Complex in South Africa, the Sudbury deposit in Canada, as well as from Finland, Russia (Urals), Italy, Greece, and Australia.

Rarity

Very rare

For collectors

## Quality criteria The quality of an orcelite specimen is determined not by the mineral itself, which is microscopic, but by the abundance of its occurrence in the host rock and the presence of well-documented associated minerals. Specimens from the type locality (New Caledonia) are the most prized. Its collectible value is primarily scientific, and specimens are sought after by specialized collectors of rare minerals and research institutions. ## Popular localities The most known and valued specimens come from the Tiébaghi chromite mine in New Caledonia.

Care and storage

## Cleaning It usually occurs as fine inclusions in the host rock, so cleaning the mineral itself is neither possible nor necessary. The rock specimen can be cleaned with a soft, dry brush to remove dust. ## What to avoid Avoid contact with acids and strong chemicals, which can react with arsenides. Due to its arsenic content, avoid inhaling dust during any mechanical processing and wash hands after contact with the mineral. ## Storage Specimens containing orcelite should be stored in a dry place, in sealed containers or display cases, to protect them from dust and contaminants. The specimen should be labeled due to its arsenic content.