Meteorwrongs are rocks which people think are meteorites, but turn out to the ordinary terrestrial rocks. The term “meteorwrong” is a play on words with “meteorite,” rather than an official term in geology. Meteorwrongs are often easy to identify with a casual glance, and some colleges and rock hounding associations offer clinics to identify rocks and show people how to spot meteorwrongs.
There are several reasons to want to identify a rock as a meteorite. Many people find meteorites interesting, because they come from space, and sometimes collectors will pay a high price for verified meteorites. Scientists are also sometimes interested in these rocks, because they can provide information about how the universe developed, and what sort of minerals can be found in abundance in space. Sometimes the identification of a meteorite also becomes important in court, as for example when someone claims that meteorite damage to a home should be covered by insurance.
Many people have an idea of what a meteorite looks like, and when they find rocks which fit with this mental picture, they may decide that these rocks are meteorites. In fact, most of the time they are plain old Earth rocks like iron debris, magnetite, and vesicular basalt, much to the disappointment of their discoverers.
So, how does one tell if a rock is a meteorite or a meteorwrong? Sometimes, it requires the assistance of a skilled geologist, but there are a few major clues which can lead you in the right direction. One of the defining features of a meteorite is a fusion crust, caused by passing through the Earth's atmosphere at high speed. The fusion crust is black to rusty brown in color, depending on age, and typically very smooth. It also looks very different from the rest of the rock, once it is cut open.
Most meteorites are highly magnetic, and dull in color. If a rock is covered in crystals, especially brightly colored ones, it is most likely a meteorwrong. True meteorites are extremely dense, feeling very heavy for their size, and they are often flecked with small pieces of metal. Meteorwrongs have gas bubbles, air pockets, and large pieces of sediment, often in layers.
One of the biggest clues is the surrounding geologic material. If you find neighboring rocks which look more or less identical, you are holding a meteorwrong, and while the rock might be interesting or valuable for other reasons, it certainly isn't from outer space.
For collectors who want to avoid meteorwrongs, it is a good idea to ask for an independent appraisal of a rock which someone claims is a meteorite. Many geologists who specialize in meteorites offer appraisals, for a fee, and if the rock turns out to be worthless, it can be a fee well-spent.