A meteorite is a natural object originating in space that survives its fiery descent through the Earth’s atmosphere to land on the surface. These fragments of asteroids, comets, or even other planets provide primitive material for scientific study. Knowing the specific characteristics that distinguish them from ordinary terrestrial rocks is the first step in identification. Identification relies on a series of simple tests and careful visual examination of distinct surface and internal features.
Initial Screening: Simple Tests for Identification
The initial screening involves two straightforward tests that quickly filter out most common terrestrial rocks. The first and most telling test is for magnetism, as nearly all meteorites contain a significant amount of iron and nickel metal. This high metal content means that a standard refrigerator magnet, or preferably a stronger neodymium magnet, will be attracted to the specimen. Stony meteorites, known as chondrites, may only show a weak attraction, but the presence of iron-nickel metal is a near-universal trait.
The second immediate test relates to density, which is a measure of how heavy a rock is for its size. Because most meteorites are rich in dense iron and nickel, they generally feel significantly heavier than a similarly sized terrestrial rock. Iron meteorites, for example, can be up to 3.5 times as heavy as typical earth rocks of the same volume.
Key Physical Characteristics of Meteorites
Once a specimen has passed the preliminary tests, closer inspection of its unique physical features is necessary to confirm an extraterrestrial origin. A freshly fallen meteorite will possess a fusion crust, a thin, dark, glassy rind formed when the rock’s outer layer melts from the intense heat of atmospheric friction. This crust is typically less than two millimeters thick, often appearing black and matte or slightly shiny. On older finds, this crust may be weathered to a rusty-brown color or partially flaked away.
The surface of many meteorites, especially iron types, displays distinctive depressions called regmaglypts. These indentations resemble thumbprints pressed into clay and are caused by the ablation, or melting and scouring, of the rock’s surface during its high-speed atmospheric flight.
If the specimen is broken or cut, its interior can reveal further details, particularly the presence of chondrules. Chondrites, the most common type of meteorite, are defined by these small, spherical, grain-like inclusions, which represent some of the oldest solid material in the solar system. Additionally, a freshly broken surface of any iron-bearing meteorite will often show bright, shiny flecks of metallic iron and nickel scattered throughout the rocky matrix.
Common Terrestrial Look-Alikes
The vast majority of suspected meteorites are common rocks or man-made materials, often termed “meteorwrongs.” One frequent culprit is slag, a glassy, often magnetic, by-product of industrial smelting operations. Unlike true meteorites, slag often contains vesicles—small holes or bubbles created by trapped gas escaping from cooling molten material. Meteorites, with rare exceptions, do not contain these gas bubbles.
Two common terrestrial minerals, hematite and magnetite, are frequently mistaken for meteorites because they are dense and magnetic, respectively. A simple streak test can differentiate them. By rubbing the rock on unglazed ceramic tile, hematite will leave a distinctive reddish-brown streak, and magnetite will leave a black or gray streak. A genuine meteorite, however, will typically leave no streak or a very faint gray one.
Next Steps for Professional Verification
If a specimen exhibits the characteristic magnetism, density, and visual features like a fusion crust or regmaglypts, the next step is to seek professional verification. It is important to preserve the specimen exactly as it was found, avoiding any cleaning, polishing, or chemical alteration. Storing the rock in a clean, dry, non-metallic container, such as a plastic bag or aluminum foil, prevents further contamination or oxidation.
Thorough documentation of the find is necessary for official classification. This includes recording the precise location, ideally with GPS coordinates, the date, and the circumstances of the discovery. The finder can contact a university geology department, a natural history museum, or a certified meteorite laboratory. These institutions have the necessary analytical tools, such as X-ray fluorescence, to definitively confirm the presence of extraterrestrial nickel and classify the rock.