Iron

Chemical formula: Fe

Native iron is a naturally occurring, crystalline form of the element iron, found mainly in meteorites and in some igneous rocks.

## Characteristics Native iron is a mineral composed almost entirely of the pure element iron, sometimes with an admixture of nickel. It occurs in two main forms: telluric (terrestrial) and meteoritic. Terrestrial specimens are extremely rare and usually form small, irregular grains or flakes within igneous rocks, such as basalts. It is much more commonly found in iron meteorites (siderites) and stony-iron meteorites (pallasites), where it can form large, massive aggregates with a characteristic internal structure (Widmanstätten patterns), visible after acid etching. ## Physical Properties This mineral is opaque, with a strong, metallic luster on a fresh surface. Its Mohs hardness ranges from 4 to 5, and its density is high, reaching 7.3-7.9 g/cm³. It is malleable and ductile, meaning it can be hammered and formed without crumbling. It exhibits strong magnetic properties, which is a key diagnostic feature. ## Colors and Varieties On a fresh fracture, native iron is steel-gray to black. The surface quickly becomes covered with iron oxides and hydroxides (rust), taking on shades from reddish-brown to black. The main varieties are related to nickel content: - **Kamacite**: a nickel-poor variety (up to 7.5%), crystallizing in the isometric system. - **Taenite**: a nickel-richer variety (above 25%), also crystallizing in the isometric system. Both varieties coexist in meteorites, forming the aforementioned Widmanstätten patterns. ## History and Name The name "iron" comes from the Proto-Slavic word *želězo and has been known since antiquity. The use of meteoritic iron for making tools and ornaments predates the Iron Age and the ability to smelt this metal from ores. The oldest known artifacts made of meteoritic iron come from ancient Egypt and Mesopotamia. As a terrestrial mineral, native iron was first scientifically described from Disko Island off the coast of Greenland. ## Applications Historically, meteoritic iron was an extremely valuable raw material for producing weapons and tools of exceptional durability. Today, native iron (both terrestrial and extraterrestrial) is primarily of scientific and collector's interest. Cut and etched plates of iron meteorites are prized decorative and collectible items.

Properties

Mohs hardness: 4-5
Luster: Metallic
Streak: Steel-gray
Density: 7.3-7.9
Cleavage: Good on {001}
Fracture: Hackly
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Native iron is most easily identified by its strong magnetism – it is one of the few natural substances so strongly attracted by a magnet. Other features include high density, metallic luster on a fresh surface, malleability, and a steel-gray streak. In the case of meteorites, the presence of a fusion crust and internal structures (Widmanstätten patterns) visible after cutting and etching are characteristic. ## Distinguishing from Similar Minerals - **Magnetite and Hematite**: Although they can be magnetic (magnetite strongly, hematite weakly), they are brittle and have a black or reddish-brown streak. Native iron is malleable and has a gray streak. - **Pyrite**: It has a similar luster, but is much lighter, brittle, non-magnetic, and has a greenish-black streak. - **Native Platinum**: It is also very dense and malleable, but much rarer, more corrosion-resistant, and has higher hardness. ## Crystal Forms Well-formed crystals of native iron are extremely rare. It usually occurs in the form of massive, compact aggregates, irregular grains, flakes, nuggets, or dendrites. In meteorites, it forms intergrown lamellae of kamacite and taenite in a characteristic, geometric arrangement.

Geological environment

## Genesis Native iron occurs in two distinct environments: 1. **Extraterrestrial origin**: It is the main component of iron meteorites (siderites) and occurs in stony-iron meteorites (pallasites, mesosiderites) and some chondrites. It forms as a result of the crystallization of an iron-nickel melt in the cores or interiors of asteroids that have fragmented. 2. **Terrestrial (telluric) origin**: It is extremely rare. It forms under strongly reducing conditions, where magma comes into contact with rocks rich in carbon or hydrocarbons (e.g., bituminous shales, coal seams). The reduction of iron oxides from the magma leads to the precipitation of pure metal. Such conditions existed, for example, in the basalts on Disko Island (Greenland) and in Bühl near Kassel (Germany). ## Mineral Associations - **In meteorites**: taenite, schreibersite, troilite, cohenite, olivine (in pallasites), pyroxene. - **In terrestrial occurrences**: cohenite, troilite, magnetite, ilmenite, pyroxene, graphite. ## Localities The most important native iron localities are associated with meteorite finds. Classic examples include Canyon Diablo (Arizona, USA), Sikhote-Alin (Russia), Campo del Cielo (Argentina), and Morasko (Poland). The most famous and largest source of terrestrial native iron are the basalts on Disko Island off the west coast of Greenland, from which blocks weighing up to 22 tons have been found. Other confirmed localities include the vicinity of Kassel in Germany and some magmatic intrusions in Russia (Siberia).

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of native iron depends on its origin and form. - **Meteorites**: The most highly prized specimens are those with a well-visible fusion crust, an interesting shape (regmaglypts), and, in the case of cut and etched plates, a clear and aesthetic pattern of Widmanstätten figures. Large, complete specimens from known falls command very high prices. Fragments of pallasites with transparent olivine crystals embedded in a metallic matrix are particularly sought after. - **Telluric iron**: Due to its extreme rarity, every documented specimen has high scientific and collector value. The most valuable specimens are from classic localities, such as Disko Island, especially if they show crystalline forms or are embedded in the original host rock (basalt). ## Market Prices The prices of iron meteorites range from a few cents to several dollars per gram for common finds, up to tens or hundreds of dollars per gram for rare types or historically significant specimens. Telluric iron specimens appear on the market extremely rarely, and their prices are set individually, often reaching very high levels due to their uniqueness.

Care and storage

## Cleaning Native iron specimens, especially meteorites, are very susceptible to oxidation (rusting). Cleaning should be kept to an absolute minimum. Fine dust can be removed with a soft brush or compressed air. If rust removal is necessary, specialized, anhydrous chemical methods are used (e.g., in professional conservation laboratories). Water or acids should never be used. ## What to Avoid The biggest enemies of native iron are moisture and oxygen. Avoid storing in damp rooms (e.g., basements) and places with large temperature fluctuations, which promote water vapor condensation. Contact with water, acids, salts (including sweat from hands) leads to rapid and often irreversible corrosion. ## Storage Specimens should be stored in a dry environment, preferably in sealed containers (e.g., plastic) with a desiccant (e.g., silica gel). For valuable meteorites, special display cases with controlled atmospheres (e.g., nitrogen-filled) are used. To prevent further oxidation, the surface of the specimen can be coated with a thin layer of specialized mineral oil or microcrystalline wax.