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MARTIAN METEORITE NWA 1460 FOUND IN MOROCCO
Dr. Anthony Irving
University of Washington
February 12, 2003

                          NWA 1460
           [Image]                       [Image]

   Image 1: Shergottite NWA      Image 2: Cut face of NWA
 1460 complete stone, showing      1460, showing yellow
 fresh fusion crust and part    pigeonite grains and dark
  of interior. Photo © Adam     maskelynite laths. Photo ©
       and Greg Hupe.                 Nelson Oakes.

A 70.2 gram meteorite completely coated with fusion-crust found in 
Morocco in December 2001 is almost certainly paired with basaltic 
shergottite NWA 480 (acquired in November 2000 by Bruno Fectay and 
Carine Bidaut). Small fragments from one end of the new stone were 
sent by a Moroccan dealer to Adam and Greg Hupe, who submitted it for 
study by Drs. Anthony Irving and Scott Kuehner at the University of 
Washington in Seattle.

The complete stone (referred to as "Black Beauty") was later purchased 
by Pennsylvania collector Nelson Oakes. Like the smaller 28 gram NWA 
480 stone, this new stone is very fresh and is coarser grained than 
most other Martian meteorites. It consists mainly of large grains of 
compositionally zoned, low-Ca pyroxene (with orthopyroxene cores, 
augite mantles and pigeonite rims) and glassy, shocked plagioclase 
(maskelynite), with lesser amounts of two phosphate minerals 
(merrillite and chlorapatite), exsolved iron-titanium oxides, 
ilmenite, chromite, pyrrhotite, potassium-rich glass, silica and
baddeleyite.

A distinctive feature of both stones is the occurrence of complex 
intergrowths consisting of varying amounts of
fayalite+hedenbergite+silica along the boundaries of pigeonite grains, 
which probably represent breakdown products of former pyroxferroite 
(an iron-rich pyroxene-like mineral first found in Apollo 11 lunar 
basalts). In addition, the University of Washington scientists 
discovered crystals of baddeleyite (zirconium dioxide) associated with 
the symplectites in NWA 1460.

Baddeleyite was recently confirmed by Dr. Albert Jambon in NWA 480 as 
well, and the patterns of compositional zoning in the pyroxene grains 
of NWA 1460 match those found by Barrat et al. (2002) for NWA 480. The 
almost identical morphologies, textures and mineral compositions of 
both specimens suggests strongly that they are paired stones from the 
same fall, and the oxygen isotopic composition measured earlier for 
NWA 480 at the University of Paris confirms its Martian origin.

The new, larger stone now will permit scientists to confirm the cosmic 
ray exposure age (2.4 million years) measured by Marty et al. (2001) 
for NWA 480, and to measure accurately the age of its igneous 
formation on Mars. The unusually fresh fusion crust on both stones 
suggests that they are part of a relatively recent fall (perhaps even 
within the last century) of an ancient volcanic or shallow subsurface
igneous rock ejected from Mars by a large impact.

There is a good possibility that other stones from the same fall also 
landed in the western Sahara desert, but they may be difficult to find 
because the exact locations of the two existing stones are known only 
to the nomads who provided them to Moroccan dealers.

            [Image]                        [Image]

      Image 3: False-color          Image 4: False-color
  backscattered electron image  backscattered electron image
 showing compositionally-zoned       showing an exsolved
 pyroxene grains (orthopyroxene   iron-titanium oxide grain
    - blue; augite - green;     containing oriented lamellae
  pigeonite - red to yellow),    of ilmenite (green) within
    maskelynite (dark blue),   titanomagnetite (red). Photo ©
     merrillite (red), and        Anthony Irving and Scott
  titanomagnetite and chromite            Kuehner.
    (white). Photo © Anthony
   Irving and Scott Kuehner.

            [Image]                        [Image]

      Image 5: False-color          Image 6: False-color
  backscattered electron image  backscattered electron image
     showing a symplectitic        showing a symplectitic
         intergrowth of        intergrowth of fayalite+silica
  fayalite+hedenbergite+silica at a contact between pigeonite
 at a contact between pigeonite    and merrillite. Photo ©
 and K-Al-Si-rich glass. Photo    Anthony Irving and Scott
   © Anthony Irving and Scott             Kuehner.
           Kuehner.

            [Image]                        [Image]

      Image 7: False-color          Image 8: False-color
  backscattered electron image  backscattered electron image
  showing prismatic grains of   showing patchy compositional
  baddeleyite (bright yellow)    zoning in maskelynite (top)
       associated with a        and an interstitial grain of
  fayalite+hedenbergite+silica    silica (probably formerly
  symplectitic intergrowth and   shock-produced stishovite)
    ilmenite near a contact    containing irregular dendritic
     between pigeonite and      structures and surrounded by
  maskelynite. Photo © Anthony radial cracks. Photo © Anthony
   Irving and Scott Kuehner.     Irving and Scott Kuehner.

                           [Image]

                 Image 9: Plot of compositions
                  of zoned pyroxene grains in
                 NWA 480 and NWA 1460. Diagram
                  © Anthony Irving and Scott
                           Kuehner.

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