Angrites
The achondrites of this group are named for their type specimen, Angra
dos Reis, a meteorite that fell in Rio de Janeiro, Brazil, in early 1869.
Angra dos Reis is a unique igneous rock that is largely composed of the
rare pyroxene fassaite, an aluminium-titanium diopside. During the last
two decades, a handful of similar fassaite-rich meteorites have been
recovered, leading to the establishment of the angrite group, presently
comprising six members.
The angrites are primarily composed of varying amounts of fassaitic
pyroxene, anorthitic plagioclase, minor olivine, kirschsteinite, along
with other accessory minerals and phases. They are basaltic rocks with
cumulate textures, often containing porous areas and abundant round
vesicles with diameters up to 2.5 cm. These vesicles have been interpreted
as remnants of gas-bubbles that formed prior to the crystallization of the
rock. However, current research suggests that the vesicles originally were
solid spheres that have been exsolved in subsequent stages of
rock-formation. Both theories are consistent with a magmatic origin of the
angrites, making them the most ancient igneous rocks known. They show
crystallization ages of ~ 4.55 billion years, which suggests their
formation occurred in the early days of the unfolding solar system. The
angrites are thought to have formed on one of the earliest differentiated
asteroids from the igneous processing of CAI-rich chondritic matter,
similar to carbonaceous chondrites of the CI or CM group.
By comparing the reflectance spectra of the angrites to that of several
main belt asteroids, two analogs were identified - 289 Nenetta, and 3819
Robinson. Further research will determine whether one of these asteroids
actually represents the angrite parent body. Only three angrites are
currently available to the private collector; these are Sahara 99555, a
single stone that was found in the Sahara desert in 1999, D'Orbigny,
an Argentinian find from 1979 that wasn't recognized as a meteorite until
1998 and NWA 1670 with a total weight of only 30gr....
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Sahara 99 555
Angrite
Found in 1999, Sahara
2710 gr
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Sahara
99555-01
0.500 gr
Nice fragment for this rare type !
SOLD |
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Sahara 99555-02
0.354 gr
Nice fragment with an open window !
285 $
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Sahara 99555-03
0.540 gr
Nice fragments
SOLD
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