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 described below.

Complete 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 find.

Partial 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.

Fragments are 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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