William R. Sharp, a research professor at the Colorado School of Mines in Golden, is often asked to identify rock specimens. Here is his advice.
The quick answer is that your rock is most likely not a meteorite at all. This is based upon our experience with material brought to us for identification, assumed by the owner to be a meteorite.
Image: Views of the Solar System
Meteorites are in fact very rare occurrences. The total mass of meteorites in museums or in collectors' hands is estimated to be far less than the total yearly world production of gold (2,000 or so tons). Experts estimate between 20,000 to 100,000 tons of material from space collides with the Earth each year; however, most of it burns up in the atmosphere, becomes atmospheric dust, lands in the ocean, or is simply never found.
One opportunity for finding a meteorite is to observe a fireball and recover the resulting impact debris, which survives the explosive encounter with the Earth's atmosphere. Fireballs are rather common occurrences. However, recovering space rocks resulting from a fireball is a much rarer event, but it does occur and there are recorded incidents where homes, cars, and mailboxes have received direct hits.
A larger number of meteorites are "finds" not directly related to an observed fall. The best areas for collecting meteorites are where they "stand out" against their natural background such as in deserts or in Antarctic glacial snows. Antarctica, for example, is a particularly rich source of meteorites because they are pushed up onto the surface of the ice. The famous Allan Hills meteorite that some believe contains evidence of life on Mars was found there.
In general, the appearance and feel of a "strange looking rock" is the best indicator that it might indeed be a meteorite. Consider the following questions:
Does the rock have a black or brown sooty-looking exterior? Does the rock have a density greater than normal? Is the sample metallic or does it contain pieces of metal? Is the material different from other rocks in the area? Does the rock have a strange "fish-eye" looking texture?
An answer of yes to any of the above questions is an indication that you may be in possession of a very unique and rare rock. Further investigation may be warranted.
A recent fall will have a textured exterior resembling a charred orange skin, referred to as a "fusion crust," which results from oxidization of the object as it passes through the atmosphere. When a meteorite lies around on the Earth's surface for an extended period, the fusion crust and interior minerals will become weathered, complicating the identification process.
Most meteorites that actually crash into the Earth's surface contain metallic iron, which can be visually recognized and easily detected with the assistance of a pocket magnet. Nickel also is normally always present in iron meteorites. To identify nickel in a specimen, however, will require laboratory testing.
Meteorites contain no hazardous materials, which may be harmful to humans. This is, of course, unless, one becomes a direct target of an incoming meteorite. Because there are no recorded incidents of humans being killed by falling space rocks, we can be reassured meteorite falls are indeed rare.
Chemically and physically meteorites differ from most ordinary Earth rocks. However, no new elements or life forms have so far been detected in meteorites. Organic compounds, including the amino acids necessary for life, have been identified in some very special types of space rocks. Some researchers claim the Martian meteorite contains fossilized bacteria, but the scientific community has not yet unanimously endorsed the claim.