ABOUT METEORITES...

Meteorites are objects coming from space that land on Earth.

They are produced by the collision between asteroids that are called parent-bodies, providing fragments that are thrown away in Space. Some of those fragments will meet the Earth's orbit and land on the blue planet after falling through the atmosphere.

While crossing the atmosphere, extreme heat is produced, which will leed to several consequences:

- Loss of 60 to 80% of initial mass (before reaching the atmosphere) of the object
- Meteorites will very often break into several fragments, due to temperature gradiants between the interior temperature (- 270°C approx.) and the exterior temperature (fusion temperature).

- A fusion crust will be generated on the surface of burning meteorites. The material in fusion flowing along the surface can produce regmaglypts on the fusion crusts, looking like thumb prints on clay.

Watching the inside structure of a meteorite, here's what you can see in about 80% of cases:

The small greenish and grey spheres are called "chondrules" and contain mainly olivine or pyroxene. One can find such a mineral structure only in those stony meteorites (called chondrites), as well as the small shining flakes that are made of "native iron" (a Fe-Ni alloy). The presence of iron explains why those meteorites are attracted by a magnet, which is also a helpfull clue for a meteorite hunter on the field!

DIFFERENTIATION:

When grinding completely an ordinary chondrite, and removing all iron particles with a magnet, we obtain a stony compound which mineral composition is very similar to the one of a surface terrestrial stone (peridotite type). And when watching the proportion of iron that was extrated, it is similar to the percentage of iron contained in the Earth, which is totally located in the core.

This basic experience illustrates the differentiation theory as the process that ruled the formation of the Earth after accretion, of the other stony planets and some asteroids of the solar system.

Classification of meteorites is based on the Differentiation theory:

- NON DIFFERENTIATED METEORITES (Chondrites)

  - DIFFERENTIATED METEORITES