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Portales Valley H6

Portales Valley H6 is an odd meteorite. Since it fell in New Mexico in June 1998 researchers have worked to explain how it formed.

The metal that conspicuously separates angular silicate clasts might have come from the chondrite mass during a large impact. Another source might have contributed metal in a lesser impact if the parent body was still partially molten at the time. A clue might be the varied compositions of the metal.

Both metal and silicates show signs of slow cooling. The metal has acquired a Widmanstätten pattern. The mineral grains show only low shock levels, presumably through annealing. Crater fallback material might have insulated the shocked material from heat loss. Or continued accretion onto a young H-chondrite body might have done the same. The formation events mobilized several elements that transformed existing minerals and formed new ones.

David Weir’s excellent Portales Valley page provides details from several published studies. Ruzicka and Hutson wrote a well illustrated piece for PSRD which is a summation of the exhaustive work by Ruzicka, Killgore, Mittlefehldt and Fries.

 

 


Two metal-rich slices, a thin section and a centimeter cube.

 

 


Exposed metal “veins” at the top of this slice resemble heavy foil.

 

 


Thin section with bright metal.

 

 


Metal, sulfides and other minerals are opaque to transmitted light. Thin section backlit.

 

 


Thin section viewed in incident light. Metal is white and troilite is rose colored. Field of view is 2.4mm wide.

 

 


Vein of rose colored troilite. FOV = 2.4mm.

 

 


Same view in plane polarized transmitted light.

 

 


Same view in cross-polarized light, XPL.

 

 


This and the following photos are from several thin sections. The few remaining chondrules and chondrule fragments in this metamorphic grade 6 chondrite are mostly barred olivine.

 

 

 

 

 

 

 

 

 

 

 

 

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