Meteorites are typically very heavy, magnetic, and bear distinctive marks caused by heating as they plunge through the atmosphere.
Close-up of Hoba, one of the largest meteorites ever discovered. (Photo: Travel Telly).
Meteorites often originate from asteroids or comets, traveling through the atmosphere and landing on Earth. There are three main types of meteorites: iron, stony-iron, and stony. Each type can be further divided into smaller groups based on mineral content, structure, and chemical composition. Some meteorites, like chondrites, can be over 4.5 billion years old and are extremely rare, while more common types, such as iron meteorites, tend to appear quite frequently.
So how can one distinguish a meteorite from an ordinary rock? One way to test is to measure the specific gravity. Meteorites contain iron and other dense materials, meaning they will be significantly heavier than an ordinary rock of the same size.
Meteorites that contain a lot of iron will be magnetic, so they often attract magnets. However, this is not an infallible rule, as some rare types of meteorites may not be magnetic.
Unlike ordinary rocks formed from Earth, meteorites have many peculiar shapes after undergoing the heating process in the atmosphere. They may even bear unusual dents on their surface known as regmaglypts, which resemble fingerprints left by a potter on wet clay. These dents form when the outer layer of the meteorite melts during its descent to Earth’s surface.
This process can even create an outer coating on the meteorite’s surface known as fusion crust, which looks like a black eggshell. The surface of a fresh meteorite is usually shiny due to the impact of traveling through Earth’s atmosphere at high speeds. If it remains on the ground for a longer period, the meteorite might take on a brown color as the iron begins to rust.
Additionally, flow lines—super-fine lines formed as the meteorite melts while entering the atmosphere—can be thinner than a human hair and are another characteristic for identifying meteorites.
Flow lines on iron meteorite Taza (NWA 859). (Photo: Geoff Notkin)
In addition to checking for magnetism, individuals finding a suspicious rock can also perform a scratch test. After scratching the surface on an unglazed ceramic, meteorites do not leave a streak. Rocks that leave a black or red streak might contain magnetite or hematite, minerals that are typically not found in meteorites. However, this method is not absolutely accurate as some types of rocks also do not leave streaks.
If the resources are available, the finder could drill a hole in the specimen to see if there are any shiny metal fragments. This could indicate that the rock originated from outer space.
One can also use the process of elimination to distinguish meteorites from ordinary rocks. Meteorites do not contain crystals like quartz. Most quartz forms from cooled magma and does not come from space.
Volcanic rocks sometimes contain bubbles from this cooling process, but meteorites do not contain internal bubbles. Similarly, meteorites typically do not have vesicles—tiny cavities often found in volcanic rocks like pumice.
Laboratory testing is a way to obtain a more definitive answer regarding meteorites. Iron made by humans from smelting processes (known as metallurgical slag) can sometimes be mistaken for meteorites, but this confusion can be avoided by checking for the presence of nickel. Earthly iron typically does not contain nickel, while meteorite iron from outer space contains at least a small amount of pure nickel.
