AW: [meteorite-list] There are no silly questions? Wait until youhaveread that :-)

[star-bits at comcast.net]

<If all ungrouped iron meteorites are derived from the cores of differentiated 
bodies, the question is: 
where is all the crust gone? Why don't we have many more (at least 92) different 
types of achondrites in our meteorite collections?>

>From Mittlefehldt et al, chapter 4 p4-15  "Planetary Materials" Reviews in Mineralogy Vol 36

"cosmic ray exposure ages of iron meteorites are typically in the range of 200 to 1000 Ma, some 5 to 50 times longer than typical for stony meteorites.  Tight clusters in exposure ages for groups IIIAB and IVA suggest discrete breakup events for their parent bodies 650 +/- 75 and 420 +/- 70 Ma ago, respectively (Voshage and Feldmann 1979).  No other clusters have been observed.  The highest 41K/40K exposure age measured for an iron meteorite is 2.3 Ga, or half the age of the solar system, for the ungrouped Deep Springs iron."

    The longest CRE exposure age I know of for a non-iron is Soko-Banja at 71.1 Ma although there may be others I don't know of.   This does exclude lunars which do have CRE ages of up to a billion years.  
    So if the non-irons are swept clean in 100,000 years or less and the irons hang around for a up to a billion or more that would explain why we see more variety in iron parent bodies.

--
Eric Olson
ELKK Meteorites
http://www.star-bits.com