EUCRITE
The ÒHED meteoritesÓ (howardites & eucrites &
diogenites) are unusual rock samples from the asteroid belt (between Mars &
Jupiter) in that they have been successfully linked to a known, named parent
body. Most meteorites are simply referred to as coming from Òsome parent
bodyÓ in the asteroid belt. HED meteorites are known to have come from
the asteroid Vesta.
The most common Vestan rocks are eucrites (see sample below). Eucrites
are basalt rocks from Vesta's crust. They range in specific lithology
from non-cumulate basalt to cumulate basalt to brecciated basalt to regolith
breccias dominated by basalt clasts.
The sample shown below is from the NWA 3359 Meteorite.
It was found in northwestern Africa in 2005. ItÕs lithology is usually
referred to as a polymict eucrite, which is a Vesta regolith breccia dominated
by large, irregularly-shaped, dark-colored clasts of basalt.
Mineralogically, Vestan basalt is principally composed of pigeonite pyroxene
and calcic plagioclase feldspar (anorthite).
This particular rock has not been dated, but published
dates from other eucrites show that the primary crystallization age of Vestan
basalt is 4.565 billion years.
Eucrite
(polymict eucrite slice, 3.6 cm across at its widest). This is a breccia
dominated by large, irregularly-shaped, dark gray-colored clasts of eucrite
(Vestan basalt).
Eucrite
(polymict eucrite slice). Flip side of specimen shown above.
(More info. on the
NWA 3359 Meteorite)