What makes a meteorite

A cut and polished slab of the pallasite Imilac meteorite on display in Hintze Hall. Pallasites contain big, beautiful olive-green crystals - a form of magnesium-iron silicate called olivine - embedded entirely in metal. Sometimes the olivine does not occur as a single crystal but as a cluster. Elsewhere it can create a pattern of veins through solid metal. The scientific jury is still out on exactly how pallasite meteorites formed.

Some scientists believe they formed in melted asteroids in a similar way to iron meteorites, where dense iron metal sinks toward the centre to form an iron core. Pallasites are thought to be samples of the boundaries between a metal core and the silicate, olivine-rich mantle around it. If this is the case, they could tell us a lot about the formation of Earth and other terrestrial planets.

However, other scientists think that there are very few olivine-rich meteorites in the asteroid belt, and too many pallasite meteorites for them all to have come from a core-mantle boundary. These types of formations may also be formed by impact melting.

Mesosiderite meteorites are breccias, a variety of rock composed of broken fragments of minerals or rock cemented together by a finer material. The fragments are roughly centimetre-sized and contain a mix of igneous solidified silicate and metal clasts rocks made of pieces of older rocks. Mesosiderites form when debris from a collision between two asteroids is mixed together. In the crash, molten metal mixes together with solid fragments of silicate rocks.

Mesosiderites can therefore both record the history of both meteorites and reveal a snapshot of the conditions required for asteroids to melt and form iron cores. There are two main types of stony meteorite: chondrites some of the oldest materials in the solar system and achondrites including meteorites from asteroids, Mars and the Moon.

Both chondrites and achondrites have many subgroups based on their compositions, structures and the minerals they contain. At over 4. Chondrites have a distinctive appearance, made from droplets of silicate minerals mixed with small grains of sulphides and iron-nickel metal. Their millimetre-sized granules give chondrites their name, from the Greek 'chondres' meaning sand grains. There are many varieties of chondrite, with differences in mineralogy relating to the type of asteroid the meteorite came from.

Chondrites are the material from which the solar system formed. They have been little changed compared with rocks from larger planets, which have been subjected to geological activity. Chondrites can tell us a lot about how the solar system formed. The most basic types, known as carbonaceous chondrites, are rich in water, sulphur and organic material. They are thought to have brought volatile material to Earth when it was newly formed, helping to establish the atmosphere and other conditions required to sustain life.

Achondrites include meteorites from asteroids, Mars and the Moon. They are igneous, meaning at some point they were melted into magma. When magma cools and crystallises, it creates a concentric layered structure. Early in Solar System history, asteroids melted and the dense iron-nickel metal sank to the center to form a core - much like the Earth has a core. Iron meteorites are the samples of the cores of ancient worlds.

While they are rare among meteorites seen to fall to Earth only a few percent , they are among the most common type of meteorites in our collections, because they can be recognized long after their fall, are very different from Earth rocks, and are resistant to weathering.

One of the most distinguishing features of meteorites is the presence of the Widmanstatten pattern - the distinctive series of bands in geometric patterns. This pattern is created by the intergrowth of two different iron-nickel minerals formed during very slow cooling a few degrees every million years in the core of the asteroid.

The presence of nickel is a universal feature of iron meteorites. Meteorites range in age. The oldest particles in a meteorite, calcium-aluminum-rich inclusions from carbonaceous chondrites, have been dated at 4.

Meteorites that originate from the Moon range in age from 4. Meteorites that originate on Mars range in age from 4. These fragments of asteroids were either knocked out of their orbit of the Sun, and into Earth-crossing orbits, through collisions with other objects, or through the interaction of gravitational forces exerted by the Sun and Jupiter.

Retrieved on 20 June Smithsonian Institution mineralsciences. Arizona State University meteorites. How to Find Meteorites This step-by-step guide will show you how to locate meteorite fall sites using radar software and weather data along with info provided by reporting agencies and monitoring systems. Magnetite and Hematite- Often mistaken for meteorites because they are magnetic. The first picture is magnetite, while the second group of pictures features different kinds of hematite.

Dark black rocks- ex. Magnetism: A majority of meteorites are magnetic. Streak Test: Scratch your specimen on a ceramic tile. If it is a red or brown streak, you probably have hematite. Nickel Test: Run a chemical test for nickel. If the proportion of nickel is inside the range for meteorites, you may have a meteorite. Fusion Crust Test: Fusion crust is a thin, dark rind formed on a meteorite as it streaks through our atmosphere. It does not occur on earth rocks and will disappear over time due to weathering, but it can be seen on some fresh meteorites.

The absence of a fusion crust does not mean a specimen is not a meteorite. Regmaglypts Test: Regmaglypts, also known as thumbprints, are unique to meteorites. They are oval depressions found on many meteorites. The absence of regmaglypts does not mean a specimen is not a meteorite. Window Test: One of the last tests to perform. Create a small window to see inside. If you can see shiny metal flakes, you may have a meteorite.

Menu Audiences Clemson. Meteorite Identification. Meteoroids are what meteorites are called while still in space 5.