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Re: Iridium layers

Hello list:

I recommend to the group, if they have not already purchased or read it,
the title "T. rex and the Crater of Doom," by Walter Alvarez.  For me,
understanding the K/T boundary was one thing,  but the deeper
understanding of how Chixculab actually became an "item" in the
scientific community was another.  This book with an ISBN 0-691-01630-5,
really helps understand "boundary" issues.  By way of information
Chixculab was found by Mexican geologist in 1950, but remained obscure
until 1991, when it was then recognized as the biggest impact crater on
our planet.

Also, mineralogically speaking, iridium is very rare and there are only
about 23 known minerals that contain iridium. By way of comparison,
there are about 800 known minerals that contain aluminum, and about 1400
different mineral types known to contain oxygen.  In natural settings,
iridium commonly occurs with the platinum minerals, which are:
palladium, iridium, osmium, rhodium and ruthenium.

Matt Morgan's question about the global distribution or iridium could
best be answered in the context of the global distribution of platinum
deposits, in which iridium is typically found.  The main producers of
this element  and its minerals are the countries of: the Republic of
South Africa, some Ural Mt. areas, Canada (Ontario area), Columbia and
Peru.   A publication called "The Mineralogical Record" could no doubt
embellish my own condensed version of this information immensely.  (An
Arizona publication)

So... perhaps the best answer to the question "However, I was wondering
in any other strata (layers of rock) that are anomalously high in Ir are
globally distributed, such as the K/T boundary" asked by Matt Morgan,
the answer is "yes. " Iridium deposits seem to be random and linked with
platinum,  but the "other" materials found at these K/T areas are the
big pointers to an extraterrestrial culprit.

If anyone would like a list of solar system abundances of the elements
in order of greatest to least, let me know. The workup for this table is
based on Jim Grevesse's work on this subject et al. 1996.  On a ranking
of 83 elements selected from the periodic table, iridium ranks 48th in
abundance, and platinum 40.  It is still considered, however, to be very
rare.  All of this is discussed in detail in the work: "Elements of the
Universe", available from me, for those interested.

My best to the group,
Sarah Kennedy
Jensan Scientifics
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