Schreibersite

Chemical formula: (Fe,Ni)₃P

Schreibersite is an iron-nickel phosphide, found almost exclusively in iron meteorites, where it forms characteristic, metallic inclusions.

## Characteristics Schreibersite is an iron-nickel phosphide, a mineral almost never found in terrestrial rocks, but characteristic of meteorites, especially iron meteorites (siderites) and stony-iron meteorites (siderolites). It occurs as metallic, silvery-white or brownish inclusions within the iron-nickel alloy matrix (kamacite and taenite). Crystals are usually small, acicular, prismatic, or platy, often with irregular shapes. On polished and etched meteorite surfaces, schreibersite is visible as bright, sharply defined structures, often highlighting Widmanstätten patterns. ## Physical Properties This mineral is hard and brittle. Its Mohs hardness ranges from 6.5 to 7, making it harder than most metals. It has a high density, approximately 7.0-7.5 g/cm³, which is typical for metallic minerals. It is opaque and exhibits a strong, metallic luster. It is also magnetic. ## Colors and Varieties Schreibersite ranges in color from silvery-white through tin-white to yellowish and brown. A darker shade is often the result of surface oxidation. No distinct color or commercial varieties are recognized. The synonym "rhabdite" is sometimes used to refer to its rod-like crystals found in meteorites. ## History and Name The mineral is named in honor of the Austrian naturalist Carl Franz Anton von Schreibers (1775-1852), director of the Natural History Museum in Vienna, who was a pioneer in meteorite research. The name was given in 1848 by the Austrian scientist Adolf Patera. Schreibersite was one of the first minerals identified in extraterrestrial material. ## Applications Schreibersite has no industrial applications. Its significance is purely scientific and collectible. As an accessory mineral in meteorites, it provides information about the conditions prevailing in the interiors of planetesimals from which meteorites originate. It is also an object of interest for astrobiologists, as phosphorus, a key element for life, may have been delivered to early Earth in the form of schreibersite.

Properties

Mohs hardness: 6.5-7
Color: Silver-white to tin-white, tarnishes to brass yellow or brown
Luster: Metallic
Streak: Gray
Density: 7.0
Cleavage: Perfect on {001} imperfect on {010} or {110}
Fracture: Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Schreibersite is primarily identified based on its context of occurrence – its presence in iron or stony-iron meteorites. On polished and etched surfaces of these meteorites, it forms characteristic, bright, sharply defined inclusions, often with acicular or hieroglyphic shapes. It is distinguished by its metallic luster, hardness (scratches glass), and magnetic properties. ## Distinguishing from Similar Minerals Schreibersite can be confused with other metallic minerals found in meteorites: - **Kamacite and taenite**: Schreibersite is significantly harder and more brittle than these. On etched surfaces, it is brighter and does not react to acid like kamacite. - **Cohenite**: It is very similar but much rarer. Differentiation requires advanced analytical methods (e.g., electron microprobe). - **Troilite**: It usually has a more brownish hue and is much softer (hardness about 4 on the Mohs scale). ## Crystal Forms Schreibersite crystals are typically small, occurring as needles, rods, flakes, or plates. They often form aggregates with skeletal or dendritic structures. Within the meteorite matrix, they can take on irregular, amoeboid shapes, filling spaces between kamacite and taenite crystals.

Geological environment

## Genesis Schreibersite is a primary mineral, crystallizing directly from an iron-nickel-phosphorus melt under conditions of very slow cooling, such as those that prevailed in the cores of planetesimals and asteroids. This process lasted millions of years. It is a mineral typical of highly reduced environments with very low oxygen content. On Earth, its formation is extremely rare and limited to specific conditions, e.g., in fulgurites (formed after lightning strikes) or in metamorphic rocks subjected to phosphorus-rich solutions. ## Mineral Associations Schreibersite almost always occurs in association with minerals typical of iron meteorites. Its most common associations are: - **Kamacite** (Fe-Ni alloy) - **Taenite** (Fe-Ni alloy) - **Plessite** (mixture of kamacite and taenite) - **Troilite** (iron sulfide, FeS) - **Cohenite** (iron-nickel-cobalt carbide, (Fe,Ni,Co)₃C) - **Graphite** (C) ## Localities As a meteoritic mineral, schreibersite does not have "localities" in the traditional, terrestrial sense. It is found in all places where iron and stony-iron meteorites have fallen. Classic examples of meteorites in which large or well-formed schreibersite crystals have been identified include Sikhote-Alin (Russia), Canyon Diablo (USA), Morasko (Poland), Campo del Cielo (Argentina), Henbury (Australia), and Gebel Kamil (Egypt).

Rarity

Not very common

For collectors

## Quality Criteria The collector appeal of schreibersite specimens is inextricably linked to the quality of the meteorite itself. Most valued are large, well-formed schreibersite crystals, visible to the naked eye, especially those with sharp, acicular or "hieroglyphic" shapes. Specimens in which schreibersite forms distinct rims around troilite or graphite nodules are highly prized. For polished slices, the key is a clear contrast between the silvery schreibersite and the surrounding, etched kamacite and taenite matrix, revealing Widmanstätten patterns. ## Popular Localities Schreibersite specimens do not come from mines but from meteorite strewn fields. The most known sources of specimens with clearly visible schreibersite include: - **Morasko Meteorite (Poland)**: Known for the occurrence of large schreibersite aggregates. - **Sikhote-Alin Meteorite (Russia)**: Many fragments of this meteorite contain perfectly visible inclusions of this mineral. - **Muonionalusta Meteorite (Sweden)**: Its beautifully etched slices often display acicular schreibersite interwoven into Widmanstätten patterns.

Care and storage

## Cleaning Specimens containing schreibersite, especially meteorite fragments, are generally not cleaned with water. Dust and fine contaminants can be removed with a soft brush or compressed air. All polished and etched surfaces should only be touched with gloves to avoid leaving fingerprints, which can lead to corrosion. ## What to Avoid The greatest threat to schreibersite and iron meteorites is moisture, which causes rapid corrosion (rusting). Contact with water, acids, chemical agents, and high humidity must be strictly avoided. They should not be stored in damp basements or on windowsills. Prolonged exposure to direct sunlight is not harmful, but temperature changes can cause moisture condensation. ## Storage Meteorite specimens with schreibersite are best stored in a dry environment. Airtight plastic containers (e.g., membrane boxes) or glass display cases with a desiccant (e.g., silica gel) are ideal. For polished slices, a thin layer of specialized oil or microcrystalline wax can be applied to protect them by cutting off access to air and moisture.