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Find a Meteorite: Explore Meteorites - Achondrites

Achondrites: Meteorites from asteroids that melted

When asteroids became hot enough to melt the rock and metal portions found in the chondritic type, material separated to form different types of meteorites. The rock portion of the bodies became a type of stony meteorite called the achondrites (meteorites without chondrules). These are actually igneous rocks from magmas that formed on asteroids. These asteroids became hot enough to melt from radioactive elements just after the Solar System formed (4.6 billion years ago).


Igneous Rocks (formed from melts)

The Johnstown diogenite, possibly a sample from asteroid 4 Vesta, one of the targets of the Dawn mission.
The Johnstown diogenite, possibly a sample from asteroid 4 Vesta, one of the targets of the Dawn mission.

This eucrite sample, from the Australian meteorite Camel Donga, is also a meteorite type that may be a fragment from Vesta.
This eucrite sample, from the Australian meteorite Camel Donga, is also a meteorite type that may be a fragment from Vesta.

During melting, the denser metal separated in these asteroids to form iron meteorites. The Iron meteorites are composed mainly of iron alloyed with nickel and they often contain a sulfide mineral called troilite (FeS) (something like fools gold or pyrite found on the Earth). Irons are the meteorites that are most easy to identify because they are heavier than most rocks, are magnetic, and are made of iron and nickel metal. Just like the Earth which has an iron-nickel core, the composition of irons indicates that they represent the cores of their parent asteroids.

The stony-iron meteorites or stony-irons are composed of both rocky material that formed from a magma and metallic iron-nickel. If an asteroid, contains a core, mantle, and crust, like the Earth does; then, the irons would be from the core, the stones from the crust or mantle, and the stony-irons from in-between the core and mantle. The asteroid Vesta is thought to have melted and may contain achondrite materials. The optical and infrared spectral signatures of the rocks on Vesta observed by telescopes match some of the achondrite meteorites, which suggests that some of these meteorite types (Howardites, Eucrites, and Diogenites) might come from Vesta!

Stony-irons and iron meteorites

The Dora pallasite, a sample of the core-mantle boundary from an asteroid that melted.
The Dora pallasite, a sample of the core-mantle boundary from an asteroid that melted.

The Hoba iron meteorite in Namibia. A portion of the core of an asteroid that melted.
The Hoba iron meteorite in Namibia. A portion of the core of an asteroid that melted.

The Gibeon iron meteorite. This sample of the core of an asteroid has been polished and lightly etched with acid to show the crystalline structure formed by different iron-nickel crystals.
The Gibeon iron meteorite. This sample of the core of an asteroid has been polished and lightly etched with acid to show the crystalline structure formed by different iron-nickel crystals.

- Back to Explore Meteorites
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- More about asteroids that melted
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Dawn Dictionary