Meteorites: What are they and where do they come from?

Meteorites are solid extraterrestrial material that survived passage through the Earth's atmosphere and landed on Earth. It is believed that most meteorites are probably fragments from the asteroid belt that lies between Mars and Jupiter. A small number of rare meteorites are fragments of the Moon and Mars.

Most meteorites are between 4.3 and 4.7 billion years old. Since they formed very early in the development of our solar system, they provide important clues to the formation, early history, and chemistry of other planetary bodies. Each year about 3,500 meteorites reach the Earth's surface, but only five or six are recovered after observed falls. A "fall" is a meteorite that was seen falling and then collected. A "find" is one that was not seen falling, but was identified as a meteorite after study.

There are three major types of meteorites: stoney, stoney iron, and iron. More that 90 percent of all meteorites are the stoney type, which are made up mostly of silicate (silicon and oxygen) minerals.

The stoney meteorites are further subdivided into several smaller groups. Stoney meteorites called chondrites have millimeter-sized rounded masses called chondrules. The Portales Valley meteorite is an H type chondrite. This means it contains the silicate minerals olivine and bronzite along with some nickel-iron alloy. Achondrites are stoney meteorites that lack these rounded masses. Iron meteorites consist mainly of an iron-nickel alloy. Stoney irons have characteristics of both the stoney and iron types.

Examples of a stoney (chondrite) and two iron meteorites are on display in the Miles Mineral Museum in Roosevelt Hall on the ENMU campus. A sample of the Macy meteorite found near Floyd was donated to the museum by Skip Wilson of Portales. A fragment of the Canyon Diablo meteorite that produced Meteor Crater in northern Arizona was also donated by Skip Wilson.

Another iron meteorite was recently verified and prepared for display. A cut surface on this meteorite was polished and etched to reveal the beautiful pattern produced by the intergrowth of the iron-nickel alloys. Anyone with a suspected meteorite is encouraged to bring it by for verification.