[meteorite-list] E chondrites

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:25 2004
Message-ID: <3C83E24F.88657BAB_at_lehrer1.rz.uni-karlsruhe.de>

Jeannie wrote:

> I had someone ask me about a meteorite that perhaps
> originated from Mercury, or the orbit of Mercury...


Hi Jeannie and List,

Although O.R. Norton's wonderful new book on meteorites is
to be released in North America on April 1, there is still a lot of
invaluable information in RFS I and II - but who am I telling that :-)

NORTON O.R. (1998) Rocks From Space, p. 190, E-Chondrites:

E-chondrites are rare, representing less than 2 % of the stony
meteorites, and only twenty-four(*) are known. They must have
formed in an oxygen -depleted environment, since most of their
iron occurs either as metal or in combination with sulfur, forming
the iron-sulfide mineral troilite.
In ordinary chondrites, pyroxene contains both magnesium and
iron in a ratio depending on the availability of oxygen. Not so the
E-chondrites. Their pyroxene contains no iron, only magnesium.
This almost pure magnesium silicate pyroxene is called enstatite,
and accounts for about 65 percent of the mineral content of these
meteorites. Thus, they are called enstatite chondrites, or E-chondrites.
It's not surprising to see a fayalite content of less than 1 %. Like the
ordinary chondrites, E-chondrites are subclassified into H and L types
depending on total iron. EH-chondrites have more total iron (about 30
percent) and more metal. EL-chondrites have less total iron (about 25
percent) and less metal.
Their low oxygen content suggests that they formed even closer
to the Sun than the H-chondrites, possibly inside Mercury's orbit.


Best wishes,

Bernd

(*) Meanwhile, four years later there are:

088 Non-Antarctic E chondrites in my databases
      (not included are the recent Hot Desert Finds)
210 US-Antarctic E chondrites
035 Jap-Antarctic E chondrites (incomplete data records)

As usual, this statistical obverview does not take into
consideration the (tentatively) paired specimens.


Best regards,

Bernd
Received on Mon 04 Mar 2002 04:08:31 PM PST