ordinary chondrites

METEORITE OR METEORWRONG?

ordinary chondrites

About 63%* of all known meteorites are ordinary chondrites. Below are some photos of sawn faces of some ordinary chondrites in the Washington University collection. Click on the left-hand image for enlargement. The brightest materials in each photo are metal grains (veins in Richarton). Most ordinary chondrites contain metal and are consequently magnetic.

Identified as "Richarton, ILL." possibly Richardton H5 (North Dakota, fall, 1918). In the closeup on the right,
saw marks are visible in the metal vein. Notice that the metal grains are typically less than 1 millimeter in size.

Allegan H5 (Michigan, fall, 1899)

Mocs L6 (Romania, fall, 1882). In the closeup on the right, saw marks are visible in the metal grains.

Bjurböle L/LL4 (Finland, fall, 1899)

Unnamed Northwest Africa (NWA) H5 chondrite

Ordinary chondrite pebbles found in the Sahara desert. Most are broken, but a partial fusion crust is intact on many of them. Notice that despite that all of them contain metal, they are not rusty colored.

Three views of the same stone, another unnamed ordinary chondrite (probably H chondrite) from northwest Africa.

Above left: The unspectacular weathered exterior in direct sunlight.

Above right: A polished, sawn face in direct sunlight. All the dark areas are alteration (rust) around the metal grains.

Right: The same face illuminated by a north-facing window. The metal grains are more obvious in this view. The rock looks grayer than it actually is in this view because of the polish and blue lighting.

It is likely that this meteorite fell thousands of years ago.

This meteorite violates a number of the recognition principles that I stress in "A Photo Gallery of Meteorwrongs." There is no obvious fusion crust. The surface is not glassy or shiny; there are no regmaglypts. The exterior has some ridges and one point. It's clearly a broken fragment of a larger meteorite. If you look closely at the image on the upper left (click on image to enlarge), however, there are shiny metal grains along all the protuberances (points, ridges) because these areas have been abraded from handling. Also, the specific gravity is 3.42, well within the range of ordinary chondrites.

On the right is one of many fragments of an L5 ordinary chondrite from Algeria known as Northwest Africa 869. On the top, the fusion crust is still intact. Notice that it is smooth with no holes. The rougher portion on the bottom of the photo is where the fusion crust as broken off after it fell. This meteorite probably also fell thousands of years ago and has been exposed to harsh conditions in the desert.

Note that there is no obvious metal. L chondrites don't contain as much metal as H chondrites. The rock is moderaly magnetic, however.

Click on image for enlargement (big).

Above left and right: Two views (direct sunlight) of an unclassified ordinary chondrite fragment from the Sahara desert. The fusion crust is dark and smooth. If this were a fresh fall, it would be shinier. In most meteorites the fusion crust is darker than the interior.

On the right is the weathered, broken face of the meteorite (electronic flash lighting). Rusting of the metal grains has led to reddish staining. Up close, shiny, unrusted metal grains stick out. Click on image for enlargement (big).

Two views of a sawn slice of Independence L6 (Missouri, fall, 1917), with electronic flash lighting (above, with millimeter ticks on scale) and natural sunlight (below). Click on image for enlargement. Thanks to karl Aston for the sample.

carbonaceous chondrites

Only about 2.5%* of all meteorites are carbonaceous chondrites. Allende (below) is one of the most famous of carbonaceous chondrites because it was observed to fall (February 8, 1969) and it was large (more than 2 tons). Carbonaceous chondrites are only weakly magnetic.

Allende CV (Mexico, fall, 1969), broken face (left) and sawn face (right). On the left, some chondrules have been plucked out, but in the lower right corner one is seen in positive relief. Click on images for enlargement.

*See our density web page for a tabulation of the relative abundance of different kinds of meteorites.

Prepared by:

Randy L. Korotev

Department of Earth and Planetary Sciences
Washington University in St. Louis

Please don't contact me about the meteorite you think you’ve found until you read this and this.

e-mail: korotev@wustl.edu