A meteorite is a rock from outer space that survived its fiery passage through Earth’s atmosphere to land on the surface. These extraterrestrial rocks are fragments of asteroids, comets, or even other planets, offering unique insights into the solar system’s formation. Finding a meteorite is uncommon, making each discovery a moment of scientific excitement. This guide outlines characteristics and simple tests to identify if a rock you found might be a piece of space history.
Key Characteristics of Meteorites
A distinguishing feature of a freshly fallen meteorite is its fusion crust, a thin outer layer formed as the rock’s surface melts from extreme heat during atmospheric entry. This crust is typically dark, ranging from charcoal black to dull gray, and can appear smooth, glassy, or velvety. It often shows subtle flow lines or small cracks, resembling a ceramic glaze, and is usually one to two millimeters thick.
Many meteorites display regmaglypts, which are distinctive thumbprint-like indentations on their surface. These depressions form due to the ablation process, where turbulent air currents and molten material sculpt the rock as it plunges through the atmosphere. While some meteorites may have a smooth surface, these features are unique to meteorites.
Meteorites are dense and feel heavier than typical Earth rocks of comparable size. This is due to their iron and nickel content, which are denser than common terrestrial minerals. For instance, iron meteorites have a high density, often between 7 to 8 grams per cubic centimeter, while stony meteorites typically range from 3.0 to 3.7 grams per cubic centimeter.
Meteorites usually have irregular shapes, often appearing angular with rounded edges, rather than being perfectly spherical. They generally lack vesicles, which are small gas bubbles or holes commonly seen in volcanic rocks on Earth. While some rare meteorites might contain microscopic vesicles within their fusion crust, large, obvious holes are a strong indicator that a rock is not a meteorite.
Simple Tests for Identification
A test for a suspected meteorite involves checking its magnetism, as most meteorites contain metallic iron and nickel. You can use a strong magnet; if the rock is a meteorite, the magnet will often stick to it, though the attraction can vary from strong to subtle. It is advisable to use a common ceramic magnet rather than a rare-earth magnet, as the latter can be too powerful and attract many terrestrial rocks.
Another useful test is the streak test, performed by rubbing the rock across an unglazed ceramic surface, like the bottom of a coffee cup or a tile. A true meteorite will leave no streak or, if heavily weathered, a very faint gray or brown mark. This differs from common iron-rich terrestrial rocks, which often leave distinct colored streaks, such as reddish-brown for hematite or black for magnetite.
You can perform a density comparison by holding the suspected rock in one hand and a known terrestrial rock of similar size in the other. If the suspected rock feels noticeably heavier for its size, it could be a meteorite, given its higher density compared to many Earth rocks. This simple “heft test” provides an initial indication.
Common Terrestrial Look-Alikes
Many terrestrial rocks are mistaken for meteorites due to similar appearances or properties. Slag, an industrial byproduct from metal smelting, is a common “meteor-wrong”. It can be dark, dense, and magnetic due to its iron content, but slag often has a glassy texture and contains numerous gas bubbles or vesicles, which are generally absent in meteorites.
Hematite and magnetite are naturally occurring iron-rich minerals often confused with meteorites. Both are dense and can be magnetic, with magnetite being strong. Unlike meteorites, hematite leaves a distinct reddish-brown streak, and magnetite leaves a black streak when rubbed on an unglazed ceramic surface. These minerals lack the fusion crust and regmaglypts characteristic of meteorites.
Volcanic rocks, such as basalt, can resemble meteorites because they are dark and dense. Volcanic rocks typically have porous textures with many gas bubbles (vesicles) formed during their cooling process. They do not possess a fusion crust or the metallic flecks often visible in some stony meteorites, which helps differentiate them from true space rocks.
Next Steps for a Suspected Meteorite
If your rock exhibits several characteristics consistent with a meteorite after these initial checks, handle it properly. Do not clean, grind, or break the rock, as this can destroy scientific evidence and alter its natural state. Preserving the rock as found is important for analysis.
Document your find by taking clear photographs of the rock from multiple angles, including a ruler or coin for scale. Note the precise location where it was found, including GPS coordinates if possible, as this information is valuable for scientific study.
For professional identification, reach out to experts at local universities, particularly geology or planetary science departments. Natural history museums are an excellent resource, as they often have meteorite collections and specialists who can examine your specimen. Some reputable meteorite dealers or collectors may offer identification services.