E&PS_WU_logo.jpg

 

Meteorite or Meteorwrong

Ordinary Chondrites

 

Most (>95%) stony meteorites are ordinary chondrites. Below are some photos of sawn faces of ordinary chondrites. For most of the photos, clicking on the image will bring an enlargement. The brightest materials in each photo are metal grains (veins in "Richarton"). Ordinary chondrites contain iron-nickel metal and, consequently, will attract even a cheap magnet.

 

Labeled as "Richarton, ILL." but probably 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. (Photos by Randy Korotev)

Allegan H5 (Michigan, fall, 1899). (Photos by Randy Korotev)

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

Bjurböle L/LL4 (Finland, fall, 1899) (Photos by Randy Korotev)

Two views of a sawn slice of Independence L6 (Missouri, fall, 1917), with electronic flash lighting (LEFT, with millimeter ticks on scale) and natural sunlight (RIGHT). Click on image for enlargement. Thanks to Karl Aston for the sample. (Photos by Randy Korotev)

 

Two views of a sawn slice of Cape Girardeau H6 (Missouri, fall, 1846), with electronic flash lighting from two different angles. Click on image for enlargement. Thanks to Karl Aston for the sample. (Photos by Randy Korotev)

Unnamed Northwest Africa (NWA) chondrite. (Photos by Randy Korotev)

An unnamed, probably LL, chondrite from the US. Sawn face on left, exterior with fusion crust on right. (Photos by Randy Korotev)


A large slice of Seminole (f) (H5) . There are thousands of sub-millimeter metal grains in this slice. Thanks to Phil Mani for the sample. (Photo by Randy Korotev)

A slice of Harper Dry Lake 036 (L6). Note the melt vein running through the center. (Photo by Randy Korotev)


Chondrules and metal grains on a sawn face of an unnamed chondrite (probably H5) from northern Chile. This photo was taken with natural light from a north-facing window on a sunny, clear day, so it looks a bit blue. Millimeter scale in background. (Photo by Randy Korotev)


Here's a sawn face of another unnamed (L?) chondrite showing metal grains and chondrules. This photo was taken with light from a high-intensity desk lamp. I rebalanced the color to make the gray background be gray. Millimeter scale in background. (Photo by Randy Korotev)

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. (Photos by Randy Korotev)

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 rims (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. (Photos by Randy Korotev)

 

This meteorite violates a number of the recognition principles that I stress in "Some Meteorite Realities." 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 ordinary chondrite from Algeria known as Northwest Africa 869 (L4–6). 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 do not contain as much metal as H chondrites. The rock is moderately magnetic, however.

Click on image for enlargement (big). (Photo by Randy Korotev)


 

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). (Photos by Randy Korotev)

*See the 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 that
you’ve found until you read this and this.

 

e-mailkorotev@wustl.edu

Last revised: 17 April 2019