A meteorite is an extraterrestrial rock that survives its fiery passage through Earth’s atmosphere and lands on the surface. While thousands of tons of space debris enter the atmosphere daily, only a small fraction reaches the ground intact. Finding a genuine sample is rare, often overshadowed by common terrestrial rocks. Understanding the unique characteristics imparted by its cosmic journey is the first step in distinguishing a true space rock. This guide provides practical steps for examining a suspected specimen before seeking expert confirmation.
Primary Visual Indicators
The intense heat generated by atmospheric entry leaves a distinct signature known as the fusion crust. This thin, dark rind forms when the rock’s outer layer melts rapidly and then solidifies upon deceleration. Freshly fallen meteorites typically exhibit a matte or glossy black crust, sometimes described as resembling a charcoal briquette.
This glassy layer is relatively fragile and will weather over time, often changing color to a reddish-brown as the iron content oxidizes. Observing the interior color, if visible through a chip or crack, is important: the inside material is generally lighter than the dark exterior crust. If the rock is uniform in color, it is less likely to be a meteorite.
Many meteorites display shallow indentations on their surface called regmaglypts, often compared to thumbprints pressed into wet clay. These depressions are formed by the swirling, erosive hot gases that sculpt the rock as it ablates during flight. While not present on every specimen, these distinctive pits strongly indicate an extraterrestrial origin.
The shape of the rock itself is also revealing, as the high-speed passage through the atmosphere tends to remove sharp edges and corners. A true meteorite is usually rounded and smoothed, lacking the jagged, angular features common to many terrestrial rocks.
Simple Physical and Magnetic Tests
After a visual assessment, the next step involves testing the physical properties of the suspected specimen, beginning with its density. Meteorites, especially the iron and stony-iron varieties, tend to feel significantly heavier than common earth rocks of a similar size. This unusual heft is due to the presence of metallic iron and nickel, which have a much higher specific gravity than most terrestrial minerals.
For a more objective measure, perform a specific gravity test by comparing the rock’s mass to the mass of an equal volume of water. While common terrestrial rocks often have a specific gravity between 2.5 and 3.0, stony meteorites typically range from 3.0 to 3.7, and iron meteorites can be extremely dense, reaching 7.0 to 8.0. If the rock’s density is less than 3.0, it is likely a common earth rock.
A magnet test is an immediate and effective screening tool because nearly all meteorites contain a significant amount of iron-nickel metal. Iron and stony-iron meteorites will adhere strongly to a standard magnet, while most stony meteorites (chondrites) contain enough metallic flecks to attract a strong neodymium magnet. While some terrestrial iron ores are also magnetic, a lack of magnetic attraction generally rules out a meteorite.
The streak test helps distinguish metallic meteorites from common iron ores like hematite or magnetite. By rubbing the rock against an unglazed ceramic surface, a terrestrial iron oxide will usually leave a colored streak, such as red-brown or black. Meteorites, unless heavily weathered, typically leave no streak or a very faint gray one, because the metallic iron does not powder easily.
Distinguishing Meteorites from Meteor-Wrongs
The most frequent false positives encountered by amateur hunters are termed “meteor-wrongs.” Industrial slag is the most common mimic, frequently displaying a dark, sometimes melted appearance and often containing enough metallic material to be magnetic. The key difference lies in the internal structure: slag is an industrial byproduct containing numerous small holes and cavities called vesicles, formed by gas bubbles escaping during the smelting process.
Meteorites, being solid objects formed in the vacuum of space, are typically non-vesicular, meaning they lack these bubbly holes. If a suspected rock has a spongy or porous look, it is almost certainly slag or a volcanic rock of terrestrial origin. Slag also tends to be lighter in weight than a meteorite of the same size, failing the specific gravity test.
Other common meteor-wrongs include the iron ores magnetite and hematite, which are magnetic and dense, respectively. While these rocks satisfy the magnetism or density criteria, they lack the characteristic fusion crust and the internal metallic grains seen in most meteorites. Furthermore, the red or orange rust found on terrestrial rocks is distinct from the thin, black glassy coating of a true fusion crust.
Steps for Professional Verification
Once a specimen has passed the initial screening, the next step is to seek professional verification. Proper handling and documentation are important to preserving the scientific value of a potential find. Avoid cleaning the rock with harsh chemicals or aggressively scrubbing the surface, as this can damage the delicate fusion crust or remove important surface clues.
Document the exact location, time, and circumstances of the discovery, ideally using GPS coordinates and high-resolution photographs. For professional analysis, contact a local university geology department, a natural history museum, or a reputable meteorite society. These organizations can direct the finder to specialized laboratories.
Professional verification usually involves sophisticated testing, such as X-Ray Fluorescence (XRF) analysis, which determines the precise elemental composition. A defining test is the confirmation of nickel content, as the iron in meteorites is a nickel-iron alloy, an element rarely present in terrestrial iron formations. Only a small sample is needed for conclusive laboratory procedures.