Stolperite

Chemical formula: AlCu

Stolperite is a naturally occurring copper-aluminum alloy, discovered in the Khatyrka meteorite, distinguished by its metallic luster and extraterrestrial origin.

## Characteristics Stolperite is a mineral from the native elements group, being a natural alloy (intermetallic compound) of copper and aluminum. It occurs as microscopic, anhedral (irregular) grains, usually not exceeding several tens of micrometers in size. It has been observed as inclusions in other minerals, such as khatyrkite and cupalite. Due to its size, visual features are only visible under high magnification. ## Physical Properties This mineral is characterized by a metallic luster. It is opaque. Its hardness and density have not been precisely measured due to the microscopic size of the grains, but they are estimated based on its chemical composition. ## Colors and Varieties Stolperite has a gray color with a reddish tint in reflected light. No varieties have been distinguished. ## History and Name The mineral's name honors Edward M. Stolper (born 1952), professor of geology and provost of the California Institute of Technology (Caltech), for his contributions to experimental petrology. Stolperite was approved by the International Mineralogical Association (IMA) in 2015 (IMA number 2015-038). It was discovered in a sample of the Khatyrka meteorite, found in 1979 in the Koryak Upland in the Russian Far East. ## Uses Stolperite has no commercial or industrial applications. Its significance is purely scientific and as a collector's item, as a component of a unique meteorite and an example of a naturally occurring Al-Cu alloy.

Properties

Luster: Metallic
Cleavage: None
Fracture: Hackly
Transparency: Opaque
Crystal system: Cubic

Diagnostic features

## Identification Identification of stolperite is only possible using advanced laboratory techniques, such as scanning electron microscopy (SEM) with chemical composition analysis (EDS) or electron backscatter diffraction (EBSD). Its physical characteristics do not allow for visual identification, even under an optical microscope. ## Distinguishing from Similar Minerals Stolperite occurs in paragenesis with other rare metallic minerals, such as khatyrkite (CuAl₂), cupalite (CuAl), kryachkoite ((Al,Cu)₆(Fe,Cu)), and hollisterite (Al₃Fe). Distinguishing them requires precise analysis of the aluminum-to-copper ratio and other elements in a given grain. ## Crystal Forms This mineral forms exclusively anhedral (irregular), rounded grains of microscopic size, occurring as inclusions in other mineral phases.

Geological environment

## Genesis Stolperite formed under extraterrestrial conditions, within the parent body of the Khatyrka meteorite. It crystallized from a rapidly solidifying metallic melt in an extremely low oxygen pressure (strongly reducing) environment. Its formation is linked to impact processes in space, which led to the melting and mixing of various precursor phases. ## Mineral Associations Stolperite coexists with other minerals discovered in the Khatyrka meteorite, primarily khatyrkite (CuAl₂), cupalite (CuAl), as well as decagonite, icosahedrite (the first natural quasicrystal), spinel, diopside, forsterite, and nepheline. ## Localities The only confirmed locality for stolperite in the world is the Khatyrka meteorite, found in the Koryak Mountains in Chukotka, in the Russian Far East.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a specimen, in the case of stolperite, is identical to the quality of the Khatyrka meteorite fragment in which it is found. Since the mineral is invisible to the naked eye, the collector's value pertains to the entire sample. The most valuable fragments are those with documented and studied presence of quasicrystalline phases and rare associated minerals, including stolperite. An official number from the Meteoritical Bulletin catalog enhances its value. ## Popular Localities The only source of material is the Khatyrka meteorite. Fragments of this meteorite are extremely rare on the collector's market and are mainly held by scientific institutions that have conducted research on it (e.g., Princeton University, Caltech, University of Florence).

Care and storage

## Cleaning Specimens containing stolperite (meteorite fragments) should not be wet-cleaned. Dust can only be removed using a soft brush or a photographic air blower. ## What to Avoid Avoid contact with water, chemicals, and sudden temperature changes. As a metal alloy, it is susceptible to oxidation and corrosion in a humid environment. It must be protected from moisture. ## Storage Khatyrka meteorite samples containing stolperite must be stored in a dry environment, preferably in an airtight container (e.g., a membrane box) with a desiccant (silica gel).

Sources

IMA Mineral List (CNMNC)