A meteorite is a natural object that originated in outer space and survived its impact with Earth’s surface, representing some of the oldest material in the solar system. The vast majority of rocks suspected of being meteorites turn out to be common terrestrial rocks, often called “meteor-wrongs.” While home testing cannot provide definitive proof, it is an effective and necessary process for screening a find, helping you determine if the rock possesses the fundamental characteristics that make it worthy of professional examination.
Initial Screening: Appearance and Magnetism
The first steps in testing a potential space rock involve closely examining its exterior features and its reaction to a magnet. A freshly fallen meteorite possesses a thin, dark, melted surface layer called a fusion crust, which forms from the intense heat of atmospheric entry. This crust is usually matte black or glossy and is rarely more than one to two millimeters thick, sometimes weathering to a rusty brown color over time on Earth’s surface.
The surface may also display shallow, thumbprint-like indentations known as regmaglypts, which are created by melting and ablation during the high-speed descent through the atmosphere. If a broken surface is visible, look for small, spherical grains, about one millimeter in diameter, called chondrules, which are a defining characteristic of the most common type of meteorite, the chondrite. Most importantly, meteorites do not contain large gas-formed holes or vesicles, nor do they contain the common terrestrial mineral quartz.
A strong magnet is crucial because almost all meteorites contain a significant amount of iron-nickel metal. Iron meteorites are strongly magnetic, while stony meteorites are less magnetic but will still attract a strong rare-earth magnet due to scattered metal flecks within. If your rock does not attract a strong magnet, it is highly unlikely to be a common meteorite.
Determining Density and Specific Gravity
After the initial visual and magnetic screening, a quantitative measurement of the rock’s density or specific gravity provides strong evidence. Meteorites, especially the iron-nickel types, are much denser than most common terrestrial rocks due to their high metal content. Iron meteorites have a very high density, often ranging from 7 to 8 grams per cubic centimeter (g/cm³), while stony chondrites fall between 3.0 and 3.7 g/cm³.
Specific gravity is a unitless ratio comparing the rock’s weight to the weight of an equal volume of water. To determine this at home, you need a precise kitchen scale and a method for measuring water displacement. First, weigh the dry rock in grams. Then, submerge it completely in water without letting it touch the bottom or sides, and record the new weight.
The difference between the dry weight and the submerged weight gives you the weight of the displaced water, which is numerically equal to the rock’s volume in cubic centimeters. Dividing the dry weight by this volume yields the specific gravity. If the result is below 3.0, the object is likely a common Earth rock, as most meteorites exceed this value.
Ruling Out Common Meteor-Wrongs
Many terrestrial rocks mimic the appearance and magnetic properties of meteorites, making it important to understand the characteristics of these common “meteor-wrongs.” Two of the most frequently mistaken minerals are magnetite and hematite, both iron ores that can be dense and dark. Magnetite is strongly magnetic, while hematite can be mildly magnetic, but a simple scratch test helps distinguish them from a true meteorite.
By rubbing the rock on the unglazed bottom of a piece of ceramic, like a tile or coffee cup, you can observe the color of the resulting streak. Magnetite leaves a black or gray streak, and hematite produces a reddish-brown streak, whereas a stony meteorite leaves no streak or a very faint gray one. Another common look-alike is industrial slag, a dark, magnetic by-product of smelting. Slag frequently displays a glassy, bubbly, or highly porous texture from trapped gas bubbles, a feature almost never seen in a meteorite.
Professional Confirmation: The Next Steps
If your specimen passes the home screening tests—it is dense, magnetic, lacks vesicles, and does not leave a red or black streak—the next phase is documentation and professional analysis. Record the exact location, including GPS coordinates if possible, the date of the find, and the surrounding environment. Taking high-quality, well-lit photographs of the object from multiple angles is important for initial expert review.
A definitive identification and classification can only be provided by a qualified expert using specialized equipment. You should seek out resources like local university geology departments, natural history museums, or certified meteorite laboratories and dealers for assistance. These institutions can perform non-destructive tests and, if warranted, a small cut to examine the interior structure, which is the only way to confirm the rock’s extraterrestrial origin.