Identifying a possible meteorite

Most rocks people suspect are meteorites turn out to be Earth rocks or industrial slag. This lesson gives a reliable sequence of checks and explains what only a laboratory can confirm.

The checks

Density: most meteorites are noticeably heavy for their size, because of metal. Magnetism: most are attracted to a strong magnet; a rock that ignores one entirely is unlikely to be a meteorite, though some rare types have little metal. Fusion crust: fresh falls have a thin black crust, often with fine cracks; older finds weather to brown. Shape: rounded edges, sometimes with thumbprint-like regmaglypts, but no vesicles (bubbles). Interior: a small polished corner of a stony meteorite usually shows bright flecks of metal, and often round chondrules. Streak: rubbed on unglazed porcelain, meteorites leave little or no streak; red-brown suggests haematite and black suggests magnetite.

Meteorwrongs

The commonest impostors are slag (glassy or bubbly waste from metal smelting, often magnetic), haematite and magnetite (dense iron oxides with tell-tale streaks), basalt and other dark volcanic rocks, iron-rich concretions, and manufactured metal. Desert varnish can give an ordinary rock a dark, shiny coat resembling a crust. No single test is decisive: a genuine candidate passes several checks at once.

Getting it verified

Confirmation requires a specialist: a thin section or polished mount under the microscope, and analysis of mineral compositions and, for metal, nickel content. Many museums and universities will give an initial opinion from good photographs. Do not cut, drill, heat or use acid on a specimen, and keep a record of where and when it was found, which is essential for classification and greatly increases its scientific value.

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