Size, Weight and Form
Most Americans are not familiar
with the metric system and even for people who grow up using the system it can
be difficult to envision what 20 or 100 grams of a meteorite might look like.
For the sake of comparison, a U.S. quarter dollar coin weighs 5.67 grams and is
2.43 centimeters in diameter; a golf ball size iron meteorite would weigh
roughly 200 grams.
In addition to comparative
rarity, the form of a meteorite specimen can also affect it's value. Meteorites
are sold in several forms including complete specimens, fragments and slices
specimens are meteorites that may be the remains of an unbroken
preatmospheric mass or a fragment that broke off while the meteorite was still
in incandescent flight. Complete specimens will show large areas of primary
fusion crust, some secondary fusion crust and
ablation flow lines. Oriented specimens are meteorites that stabilized while
passing through the atmosphere and show aerodynamic shaping that is the result
of material ablating (melting) off the front and flowing to the back of the
specimen. Complete, oriented specimens are very desirable and very hard to
specimens are significant pieces of complete specimens with one cut
and polished surface or a naturally broken surface which did not begin the
formation of a secondary fusion crust.
pieces of meteorites that were torn off the main mass by the extreme stresses
of atmospheric passage and the temperature differential between the
incandescent surface and the near absolute zero of the interior. If the
meteorite breaks up just before dark flight (no longer a meteor) or on impact
with the ground there is no time for a secondary fusion crust to form a
possible new complete specimen. Fragments can also be the result of improper
cutting, but some meteorites are known only in the fragment form.
Slices are sold
in complete and partial slice forms. Partial slices have at least one straight,
cut edge or a broken edge, while complete slices are cross sections of a
complete specimen with all edges presenting the outside surface of the
meteorite. Well prepared slices are usually 2-7 millimeters thick (a uniform
thickness for a given slice) and should have at least one polished surface.
Polishing is not done to a mirror finish, but to a fine enough grit to show
clear details of the interior structure. Slices are a common form purchased by
collectors, because they are less expensive than complete specimens and show
the detail of chondrules,
breccia or Widmanstätten patterns in
the various classifications of meteorites.
End pieces are
very much like the heel of a loaf of bread. They are slices cut from the
outside of a meteorite and have one cut, polished surface, while the back
surface is the outside surface of the meteorite. End pieces vary greatly in
thickness and represent a compromise between slices and complete specimens
showing the interior and exterior details of the meteorite.
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