Rocks from space, known as meteorites, offer a tangible connection to the cosmos. While rare, the possibility of encountering one captivates many. Identifying a meteorite requires careful observation and a series of simple tests. This guide provides practical steps to help distinguish these cosmic visitors from common terrestrial rocks.
Exterior Characteristics
A meteorite’s fusion crust is a dark outer layer. This crust forms as the rock’s surface melts and ablates during its fiery descent through Earth’s atmosphere. The texture of this crust can vary, appearing glassy and smooth, or slightly rough and bubbly.
Another distinctive feature found on some meteorites are regmaglypts, which resemble thumbprint-like indentations on the surface. These depressions are formed by the melting and removal of material as the meteorite travels at high speeds through the atmosphere. Unlike most terrestrial rocks, meteorites lack sharp edges or angular shapes, appearing more rounded due to the intense ablation process. Meteorites do not contain vesicles, small holes or pores formed by gas bubbles common in volcanic rocks.
Basic Field Tests
A primary test for a potential meteorite involves a strong magnet, as most meteorites contain iron and nickel and are therefore magnetic. Both stony meteorites and iron meteorites will exhibit magnetic attraction. While some terrestrial rocks like magnetite are also magnetic, the presence of magnetism is a necessary, though not sufficient, characteristic for a meteorite.
Another useful test is assessing the rock’s density; meteorites are significantly heavier than similarly sized terrestrial rocks. This increased density is due to their high iron content. To perform a streak test, rub a corner of the rock firmly against an unglazed ceramic tile. Meteorites typically produce no streak, or a faint reddish-brown streak if oxidized iron is present.
Uncovering Internal Evidence
If a rock is suspected to be a meteorite and is subsequently broken or cut, its internal structure can reveal further evidence. Many stony meteorites contain small, spherical grains called chondrules. These millimeter-sized spheres are among the oldest solid materials in the solar system, providing strong evidence of a meteorite’s origin.
Meteorites, particularly stony ones, often contain small, shiny flecks of metallic nickel-iron. These metallic particles are distinct from the surrounding rock matrix and can be seen reflecting light. Iron meteorites, when cut and polished, display a solid metallic interior, revealing unique crystalline patterns known as Widmanstätten patterns if etched with acid.
Common Misidentifications and What to Do Next
Many terrestrial materials are frequently mistaken for meteorites due to superficial similarities. Industrial slag, a byproduct of smelting, has a dark, glassy appearance and can be magnetic, but it contains gas bubbles and lacks a fusion crust. Hematite and magnetite are iron-rich terrestrial minerals that are magnetic and dense, but they do not possess fusion crusts or the internal structures found in meteorites. Basalt, a common volcanic rock, can be dark and dense, yet it contains vesicles and lacks the metallic grains or chondrules seen in meteorites.
If, after conducting these observations and tests, you still suspect you have found a meteorite, it is important to handle it carefully. Do not clean the rock, as this can destroy important scientific evidence. Record the precise location where it was found, ideally with GPS coordinates, and take clear photographs from multiple angles. The next step is to contact a local university geology department, a natural history museum, or a reputable meteorite expert for professional identification, as they have the tools and knowledge to confirm its extraterrestrial origin.