Meteorites

A meteorite is a piece of material, usually rock, which breaks off some object in space, makes it through Earth's atmosphere and falls to the ground or into the water. Seventy-one percent of the earth's surface is water. There are three types of meteorites: stony, stony-iron and iron.

The most common type of meteorite is the stony meteorite. They are made mainly of rock. Stony-iron meteorites are made up of about 50/50 rock and metal. Iron meteorites are nearly solid nickel metal. Meteorites are the rarest form of rock to find on earth. If several thousand rocks are sent to a laboratory, maybe one or two may turn out to be a meteorite rock.

All meteorites fall through the atmosphere so fast that material on their surfaces burns off. A glassy residue is left which is called fusion crust. The color is a dark grey or black. The surface can be shiny or dull and velvety. Flow lines may be seen going across some of the meteorites from melted rock. After a long period of time, much of the fusion crust may chip off. After a long time on earth, the dark color may wear off and the orange color of the iron may be very evident.

Meteorites have irregular shapes with rounded corners. Some have pits called regmaglypts made when hot air erodes the rock on its way through the atmosphere. Iron in a meteorite must always be joined with nickel. Meteorites are very dense, not porous, even though they may have pits on their surface.

Meteorite rocks are heavier than ordinary earth rock because most contain metallic iron. Metallic iron is not found in earth rocks. Meteorites contain some metallic iron and some are solid iron. Most meteorites respond to a magnet. This is a good test to determine if a rock is possibly a meteorite. However, there are some earth rocks that also attract a magnet. Rocks containing hematite and magnetite are very common on earth and also attract magnets.

Scientists will rub a rock across a streak test plate to see if a rock is a meteorite or not. A certain color of mineral powder will remain. If the powder is brown, the rock will be a meteorite. The streak color for hematite is dark red. The color from magnetite is black. This test can be done on a piece of unglazed ceramic tile also.

The largest group of space rocks is the chondrite type of stone meteorite. Tiny grains of nickel-iron metal are scattered throughout the rock. Earth rocks do not have iron grains in them. Using a hand lens to look for these metal grains can be a good test for a meteorite.

Meteorites are thought to originate in an asteroid belt between Mars and Jupiter. They can weigh less than a gram or more than sixty tons. In early history, large meteorites hit the earth and created great craters. The Barringer Meteorite Crater in Arizona is .6 miles across and was formed by a piece of iron-nickel debris 164 feet in diameter. It is rare that a human is injured by a meteorite, but in 1954, an eight-pound meteorite crashed through the roof of a house in Alabama and severely injured a woman.

Meteorites also fall on other celestial bodies. Some have been seen on Mars and the moon. Most meteorites which fall to earth come from asteroids. Asteroids are small rocky bodies in space all the way out to the orbit of Jupiter. By analyzing a meteorite and classifying it into one of three categories, a determination can be made as to where on an asteroid the piece of rock came from. An iron or stony-iron was close to the core of an asteroid, while a stony object was closer to the surface.