Differentiated
meteorites
Those meteorites come from "differentiated parent
bodies".
Some come from the surface of such parent bodies and some other
ones from the inside, and are very different from each other:
ACHONDRITES.
Polished
section of a "Diogenite" (one of the achondrite types)
Those "chondrule less" and "iron less"
meteorites come from the surface of differentiated bodies. They
represent approxiately 7% of the falls. Those "space rocks" ressemble very much terrestrial basalts, which makes it very difficult
to identify them on the field. In this case, only the presence
of fusion crust proving that it travelled through the atmosphere
shows that we found a meteorite.
They are classified according to their calcium content:
-Achondrites rich in CaO: Angrites,Eucrites,Howardite,...
-Achondrites poor in CaO: Diogenites,Ureilites,Aubrites,..
IRON METEORITES
(SIDERITES)
Those meteorites come from the core of differentiated
parent bodies. They are nearly exclusively made of iron and nickel,
plus some few minerals. When etching a polished surface of such
a meteorite with acid, its specific crystallisation orientation
appears, called "Widmanstatten patterns":
This specific structure only exists in extra-terrestrial
bodies and correspond to an extremely slow cooling process of
the heated parent body.
Mixt
meteorites
Pallasites.
Those gorgeous meteorites are made of an iron-nickel
matrix and crystallised olivine grains. They probably come from
the limit betwwen the core and the rock mantel of a differentiated
parent body.
Mesosiderites.
They are made of a metalic matrix and included achondrite
fragments. Scientists believe that they were produced by a collisions
between "iron" parent bodies and stony differentiated
ones.
Non Differentiated Meteorites