Craters on the moon, and on Earth, are created by meteor impacts.
The terms aerolite and siderite describe types of meteorites. Meteorites are the remnants of meteoroids, or rocks from outer space, that have fallen to Earth. They are classified by their mineral composition and can be identified by a few key characteristics not found in terrestrial rocks. Meteorites are rare geological finds and the information they provide about the universe is invaluable.
Origins of Meteorites
This impact crater shows the impression a meteorite can make on Earth’s crust.
Although many people associate meteorites with “meteor showers” and “shooting stars,” they usually have a different origin and mineralogical composition. Shooting stars and annual meteor showers are ice and rock debris from comets which burn up when they enter our atmosphere. They rarely make it to the Earth in a large enough piece to be found. Meteorites are the remains of asteroids, pieces of the moon and planetary debris which are much larger and can survive entry into Earth’s atmosphere.
Meteorites can be any size and there is evidence of enormous meteors colliding with the Earth throughout geologic history. Examples are Meteor Crater in Arizona, and the Chixulub Crater in Mexico on the Yucatan Peninsula.
Types of Meteorites
Meteorites are classified by their mineral content. There are three major types: iron, stoney and iron-stoney mixed. Siderite is an example of an iron meteorite because its chemical composition consists of high concentrations of iron and nickel.
Stoney meteorites such as aerolites are mainly composed of silicate minerals. These can typically resemble terrestrial rocks.
Stoney-iron, or mixed meteorites, as their name implies, incorporate both silicate and metallic minerals.
Common Characteristics of Meteorites
All meteorites display some similar characteristics. Many of these are diagnostic and can be used to determine if a rock sample is truly a meteorite.
Because of their high iron content, meteorites are dense and heavy, and they are also attracted to magnets. It is rare to find a non-magnetic meteorite. Meteorites will also have a fusion crust, a thin black layer that is created when the materials burn as they enter the atmosphere. Flowlines created by melting at this time may also be apparent on the surface.
Stoney meteorites may contain metallic flakes of iron and are also magnetic. One particular class of stoney meteorites, the chondrites, have chondrules in them. Chondrules are small, grain-like spheres that are never found in terrestrial rocks.
Many of the rocks on Earth look so strange that it’s hard to believe they didn’t come from outer space. A few key characteristics cause amateurs to commonly mistake natural Earth rocks for something extraterrestrial.
Holes or openings in a rock, called vesicles, give people the impression of a meteorite or moon rock. Rather, these vesicles are created by escaping gas bubbles and usually form in a volcanic environment. Hematite is also commonly misidentified because of its metallic luster and smooth matrix. However, hematite is not attracted to a magnet. A granular texture will also identify a rock as terrestrial in origin.