Types of Meteorites

Stony Meteorites

Accounts for about 94% meteorites recovered on earth.

Formation: 75-90% rock-forming minerals like silicate, 10-25% of metallic elements (nickel-iron alloy), small amounts of iron sulfide

Characteristics: Stone-like appearance with small flecks of metal

1) Chondrites

About 86% of all meteorites found are chondrites

Formation: Being primitive, these can contain materials that predate the formation of the solar system and planets. Having never undergoing melting, these are often studied to learn about the origin of the universe.

Characteristics: Lots of chondrules (tiny metallic or mineral grains)visible on the surface

Subdivisions: Ordinary, carbonaceous, and enstatite chondrites

Examples: Ochansk in Russia,  Allende in Mexico, Abee in Ontario museum

2) Achondrites

Younger than chondrites, these make up 8% of all meteorites recovered.

Formation: Formed due to igneous activity in planetary bodies that have distinct core and crust, like large asteroids, the moon, and mars.

Characteristics: Melting and re-crystallization eradicates ancient chondrules

Subdivisions: Howerdite, eucrite, and diogenite, together called HED meteorite

Examples: NWA 2698 in Africa, Millbillillie in Australia, Bilanga in Burkina Faso(West Africa)

Iron Meteorites

Only 5% of meteorites found on earth are this type. These are most likely to survive atmospheric entry. Resistant to weathering, they remain intact for longer, with the largest meteorites recovered on earth being of this type.

Formation: 75-95% iron, cobalt about, 5-25% nickel, and trace amounts of troilite (iron sulfide). The iron in this meteorite is one of the earliest sources of iron available to humans to forge tools and weapons.

Characteristics: Typical crystal structure (Widmanstatten structure) can be seen when cut, polished and exposed to nitric acid

1) Hexahedrites

Formation: Low in nickel content(>5.8%), no Widmanstatten structure

Examples: Boguslavka meteorite

2) Octahedrites

Formation: Low to average in nickel content (5-10%), visible Widmanstatten structure.

Examples: Sikhote-Alin meteorite in Russia

3) Ataxites

Formation: Very high nickel content (<18%), no Widmanstatten structure.

Examples: Hoba meteorite in Namibia

Stony-Iron Meteorites

Accounts for about 2% of meteorites recovered on earth.

Formation: Composed of roughly equal parts of metal (iron-nickel alloy) and stone, originates from mixing of the metallic core and rocky magma within the asteroids. These are believed to have undergone melting and solidification multiple times that results in physical and chemical changes.

Characteristics: Smooth and sometimes glossy, embedded with silicates; often cut into gemstones (e.g. extraterrestrial peridot)

1) Pallasites

Formation: Solid metallic bodies of iron-nickel.  These are believed to come from a combination of core and mantle materials of asteroids.

Characteristics: Centimeter-size greenish or olive crystals embedded in the body

Examples: Brenham in United States, Imilac in the Atacama desert in Chile

2) Mesosiderites

Formation: Originates when debris from different asteroid collisions are mixed and combined.

Characteristics: In contrast to pallasite, its crystals are smaller, pale silicate minerals.

Examples: Chinguetti in Africa, Vaca Muerta in the Atacama desert in Chile